KR102442905B1 - A separator with an adhesive layer and an electrochemical device comprising the same - Google Patents

Abstract

In one aspect of the present invention, there is provided a base membrane comprising: a porous substrate, and a heat-resistant layer disposed on at least one surface of the porous substrate and comprising a plurality of inorganic particles bound by a binder; and an adhesive layer disposed on the surface of the heat-resistant layer and comprising a plurality of first organic particles bound by a binder and second organic particles having an average particle diameter larger than that of the first organic particles; The ratio of the number of the second organic particles to the number of the first organic particles is 0.04 to 0.2 to provide a separator and an electrochemical device including the same.

Description

Separator having an electrode 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 weight reduction, such as smartphones, laptops, and tablet PCs. The development of a lithium secondary battery having a large size, long lifespan, and high stability is required.

As a means for achieving the above object, a separator with micropores that separates the positive electrode and the negative electrode to prevent an internal short and facilitates the movement of lithium ions during charging and discharging, in particular, thermally induced phase separation (Thermally Induced Phase Separation) R&D on microporous membranes using polyolefins such as polyethylene, which is advantageous for pore formation, economical, and easy to meet the physical properties required for membranes.

However, a separator using polyethylene having a low melting point of about 135° C. may undergo shrinkage deformation at a high temperature higher than 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 occur, resulting in safety problems such as ignition.

On the other hand, the conventionally widely used polyolefin-based separator has weak heat resistance and mechanical strength, so when exposed to a temperature of 150° C. for about 1 hour, heat shrinkage occurs at 50 to 90%, and the function of the separator is lost. , there is a problem that an internal short circuit is highly 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 thin particles on the surface of a separator has been proposed.

However, such a heat-resistant layer leaves significant technical challenges with respect 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 including ceramic particles is formed on the surface of the porous substrate, the heat resistance of the separator is improved, but the ceramic particles included in the heat-resistant layer close the pores formed in the porous substrate, thereby reducing the breathability of the separator, Accordingly, there is a problem in that the ion movement path between the positive electrode and the negative electrode is greatly reduced, and as a result, the charging and discharging performance of the secondary battery is greatly reduced.

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 also be gradually reduced.

On the other hand, an attempt to improve the adhesive force with the electrode and thus the lifespan characteristics of the secondary battery by additionally forming an adhesive layer including a PVDF-HFP copolymer, etc., on the conventional polyolefin-based separator or heat-resistant layer to express adhesion with the electrode was also made (Korean Patent Application No. 10-2012-0117249, etc.). However, since 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 there is a problem in that the cost of processing these volatile organic materials increases.

On the other hand, although an aqueous coating solution in which PVDF-based polymer particles are dispersed in water has been developed and applied, PVDF-based polymer particles exist in a particulate form even after the coating solution is dried, so PVDF-based polymer particles included in the adhesive layer as in the heat-resistant layer. The air permeability of the separator is reduced by closing the pores formed in the porous substrate and/or the heat-resistant layer, and accordingly, the ion movement path between the positive electrode and the negative electrode is greatly reduced, and consequently the charging and discharging performance of the secondary battery is greatly reduced. .

SUMMARY OF THE INVENTION 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, adhesion, air permeability, and conductivity in a balanced manner.

In one aspect of the present invention, there is provided a base membrane comprising: a porous substrate, and a heat-resistant layer disposed on at least one surface of the porous substrate and comprising a plurality of inorganic particles bound by a binder; and an adhesive layer disposed on the surface of the heat-resistant layer and comprising a plurality of first organic particles bound by a binder and second organic particles having an average particle diameter larger than that of the first organic particles; A ratio of the number of the second organic particles to the number of the first organic particles provides a separation membrane of 0.04 to 0.2.

In an embodiment, the number of the first organic particles may be 10,000,000 to 100,000,000/mm ² , and the number of the second organic particles may be 1,000,000 to 10,000,000/mm ² .

In one embodiment, the ratio of the weight of the first organic particles to the total weight of the first and second organic particles may be 0.3 to 0.7.

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 an embodiment, the content of the inorganic particles in the heat-resistant layer may be 60 to 99% by weight, and the content of the first and second organic particles in the adhesive layer may be 50 to 99% by weight.

In one embodiment, the thickness of the heat-resistant layer may be 0.1 ~ 5㎛, the thickness of the adhesive layer may be 0.5 ~ 1.5㎛.

In an embodiment, a ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer may be 0.15 to 0.5.

In an embodiment, the first organic particles may include a fluorine-based polymer having an average particle diameter of 50 to 300 nm, and the second organic particles may include an acrylic polymer having an average particle diameter of 350 to 1,000 nm.

In one embodiment, the separation membrane may satisfy one or more of the following conditions (i) to (vii).

(i) air permeability 210-350 sec/100ml; (ii) Rs ≤ 110 mΩ (Rs is the resistance of the separator); (iii) less than 3.0% of longitudinal heat shrinkage at 150°C; (iv) 3.0% or less of transverse heat shrinkage at 150°C; (v) 0 mΩ < Rs - Ra ≤ 20 mΩ (Ra is the resistance of the porous substrate); (vi) 0 mΩ < Rb - Rs ≤ 10 mΩ (Rb is the resistance of the basement membrane); (vii) Electrode adhesion of 1.0 gf/mm or more.

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 an aspect of the present invention includes a porous substrate, a heat-resistant layer, and an adhesive layer, but the areal density and the ratio of organic particles included in the adhesive layer are not measured by the weight of the organic particles, but through a scanning electron microscope (SEM). By specifying based on the number of observables, heat resistance, adhesion, breathability, and conductivity can be implemented in a balanced way.

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

1 is an SEM image of a plane of a separator according to an embodiment and a comparative example 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 several different forms, and thus 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 "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

In one aspect of the present invention, there is provided a base membrane comprising: a porous substrate, and a heat-resistant layer disposed on at least one surface of the porous substrate and comprising a plurality of inorganic particles bound by a binder; and an adhesive layer disposed on the surface of the heat-resistant layer and comprising a plurality of first organic particles bound by a binder and second organic particles having an average particle diameter larger than that of the first organic particles; A ratio of the number of the second organic particles to the number of the first organic particles provides a separation membrane of 0.04 to 0.2.

The porous substrate may include a plurality of pores having a substantially uniform average size, and these pores may contribute to improvement of resistance properties and ionic conductivity of the separator. In addition, the separation membrane can be thinned to a required thickness due to high porosity and high mechanical strength.

The porosity of the porous substrate may be 30 to 90% by volume, preferably, 40 to 80% by volume, more preferably, 40 to 70% by volume. As used herein, the term "porosity" refers to 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 ionic 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 the pores included in the porous substrate may be 10 to 100 nm, preferably, 20 to 80 nm, more preferably, 30 to 60 nm. If the average size of the pores is less than 10 nm, air permeability and ionic conductivity may be reduced, and if it exceeds 100 nm, mechanical properties such as tensile strength and puncture strength may be reduced.

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. When the thickness of the porous substrate is less than 5 μm, mechanical properties may be reduced, and if it exceeds 20 μm, air permeability and ionic conductivity may be reduced.

The porous substrate may include a polymer resin having electrical insulation, and the polymer resin may include a thermoplastic resin in consideration of shutdown characteristics. As used herein, the term “shutdown characteristic” means that when a battery is overheated and its temperature is increased, the polymer resin melts and closes the pores of the porous substrate to block the movement of ions. From this point of view, the melting point of the polymer resin or the thermoplastic resin may be 200° C. or less.

The thermoplastic resin may include, for example, 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. and preferably, at least one of polyethylene and polypropylene, and more preferably, 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 to 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 a 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 more than 450,000, the viscosity may increase and processability may be reduced, and if the weight average molecular weight of the polyethylene is less than 250,000, the viscosity is excessively low, so that the dispersibility with pore formers and antioxidants used to prepare the porous substrate is extremely low. and, in some cases, phase separation or layer separation may occur.

The porous substrate may be hydrophilized to sufficiently secure wettability of the slurry during coating of the slurry for forming the heat-resistant layer, thereby improving bonding strength between the porous substrate and the heat-resistant layer. A contact angle of the hydrophilized porous substrate with respect to moisture (H ₂ O) 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 , 15mV or more, more preferably, 20mV or more.

The hydrophilic support is, because of its high affinity with the slurry, which is essentially hydrophilic, because a hydrophilic functional group, for example, a -SO ₃ group generated on its surface and the surface of the internal pores has hydrophilicity. Since it can be easily combined with the heat-resistant layer, and its bonding strength can be strengthened, the durability of the separator can be significantly improved, and the loss of hydrophilic groups included in the porous substrate and/or inorganic particles of the heat-resistant layer is minimized, so that ions Conductivity and heat resistance can be improved.

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

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 air permeability, ionic conductivity, and resistance characteristics of the separator may be deteriorated, and the dispersibility of the inorganic particles may be reduced or the slurry During coating, workability and processability may be reduced.

The average particle diameter of the inorganic particles may be larger than the average size of the 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 and close the pores, thereby significantly reducing the breathability and ionic conductivity of the separation membrane. . The average particle diameter of the inorganic particles may be 100 to 1,500 nm, preferably, 200 to 1,000 nm, more preferably, 400 to 800 nm, but is not limited thereto.

The thickness of the heat-resistant layer may be 0.1 to 5㎛. If the thickness of the heat-resistant layer is less than 0.1 μm, a required level of heat resistance cannot be imparted, and when it exceeds 5 μm, the separator is thickened, thereby inhibiting miniaturization and integration of the electrochemical device.

The inorganic particles are, 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 It may be one selected from the group consisting of a combination of two or more thereof, but is not limited thereto.

The separation membrane may include; an adhesive layer comprising a plurality of first organic particles located on the surface of the heat-resistant layer and bound by a binder and second organic particles having an average particle diameter larger than that of the first organic particles; A ratio of the number of the second organic particles to the number of the first organic particles per unit area may be 0.04 to 0.2. The adhesive layer may also include a plurality of pores through which a fluid may pass.

As used herein, the term “organic particles” may refer to microparticles or nanoparticles including a polymer material. The first organic particles may be fine particles or nanoparticles containing a fluorine-based polymer, and the second organic particles may be fine particles or nanoparticles containing an acrylic polymer.

The fluorine-based polymer may be a homopolymer including 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 acrylic polymer is poly (meth) acrylate, polyacrylonitrile, polyacrylate, polyacrylic acid, acrylonitrile-acrylic acid copolymer, acrylamide-acrylic acid copolymer, ethylene-acrylic acid copolymer, alkyl acrylate-acrylo It may be one selected from the group consisting of a nitrile copolymer, an acrylic rubber, and a combination of two or more thereof, and preferably, an alkyl acrylate-acrylonitrile copolymer, polyacrylate, or acrylic rubber, but limited thereto it is not

The poly(meth)acrylate-based polymer may include a (meth)acrylic acid ester monomer having an alkyl group having 1 to 14 carbon atoms. In addition, the monomer includes an allyl ester, vinyl ester, unsaturated ester group or mixtures thereof, a cyano group, a carboxy group, an amine group, a monomer containing a vinyl group and/or a hydroxyl group, a styrenic monomer, and two or more of these It may further include one monomer selected from the group consisting of combinations. For example, the poly (methacrylate-based polymer) is butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) Acrylate, isopropyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, n-oxyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylic Late, lauryl (meth) acrylate, may be one containing tetradecyl (meth) acrylate as a monomer, but is not limited thereto.

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

The second organic particles including the acrylic polymer may contribute to improving the adhesive strength of the adhesive layer, but since their average particle diameter is larger than that of the first organic particles, when excessively applied, the pores formed in the adhesive layer are closed and the resistance of the separator can be increased, by appropriately mixing and applying the first organic particles in a predetermined ratio, the resistance characteristics of the separator and the adhesion to the electrode can be improved in a balanced way.

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

An average particle diameter of the first organic particles may be smaller than an average particle diameter of the inorganic particles included in the heat-resistant layer. If the average particle diameter of the first 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, the heat-resistant layer is continuously exposed to the electrolyte inside the battery Accordingly, the inorganic particles may be partially and continuously detached from the porous substrate, and thus the heat resistance of the separator may be gradually reduced.

The average particle diameter of the first organic particles may be 50 ~ 300nm, the average particle diameter of the second organic particles may be 350 ~ 1,000nm. If the average particle diameter of the first and second organic particles is less than the lower limit of the above range, the air permeability and ionic conductivity of the separator may decrease, and if the average particle diameter exceeds the upper limit, the surface area of the adhesive layer becomes small, and the adhesion and resistance properties may be reduced. , cannot effectively prevent the inorganic particles included in the heat-resistant layer from being exposed to the electrolyte.

The thickness of the adhesive layer may be 0.5 to 1.5 μm. When the thickness of the adhesive layer is less than 0.5 μm, adhesion may be reduced, and exposure of the inorganic particles included in the heat-resistant layer to the electrolyte may not be effectively prevented. Conversely, when the thickness of the adhesive layer is more than 1.5 μm, air permeability, ionic conductivity, and resistance properties may be reduced, and the separator may be thickened to inhibit miniaturization and integration of the electrochemical device.

If necessary, in order to strengthen the heat resistance of the separator, the adhesive layer may further include inorganic particles such as the heat resistant layer. A 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 when the content of the inorganic particles is excessively high, the dispersibility of the inorganic particles may be reduced or workability and workability during slurry coating may be deteriorated.

The binder refers to a material that binds the inorganic particles to each other in the heat-resistant layer and binds the first and/or second 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 is, 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 combinations of two or more thereof. , but is not limited thereto.

Preferably, in consideration of dispersibility in the aqueous coating composition and affinity for inorganic or organic particles, the binder included in the heat-resistant layer may be an acrylonitrile-based copolymer, and included in the adhesive layer The used 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. When 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 balance of heat resistance, adhesion, air permeability, ionic conductivity, and resistance characteristics of the separator. Specifically, if 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 properties may be improved, and heat resistance and adhesion may be reduced. On the other hand, when the ratio of the thickness is more than 0.5, the air permeability and resistance properties may be deteriorated, and heat resistance and adhesion may be improved.

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

In contrast, in the separator according to the present invention, the areal density of the organic particles included in the adhesive layer is specified based on the number (number) observable through a microscope, not the weight of the organic particles as in the prior art, so that heat resistance, adhesiveness, Breathability and conductivity can be implemented in a balanced way. Specifically, the separator materializes the areal density of the organic particles included in the adhesive layer based on the number (number) observable through a microscope, so that "heat resistance and adhesion" and "breathability and resistance properties" exist between trade- Trade-offs can be significantly mitigated.

A ratio of the number of the second organic particles to the number of the first organic particles per unit area of the adhesive layer may be 0.04 to 0.2, preferably, 0.05 to 0.15. In addition, the number of the first organic particles per unit area of the adhesive layer may be 10,000,000 to 100,000,0000 pieces/mm ² , and the number of the second organic particles may be 1,000,000 to 10,000,000 pieces/mm ² . In addition, a ratio of the weight of the first organic particles to the total weight of the first and second organic particles may be 0.3 to 0.7, preferably, 0.3 to 0.5.

If the number of the first organic particles per unit area of the adhesive layer is less than 10,000,000/mm ² , the heat resistance and adhesiveness of the separator may decrease, and if it exceeds 100,000,000/mm ² , the breathability, ionic conductivity and resistance properties of the separator will be reduced. can

In addition, if the number of the second organic particles per unit area of the adhesive layer is less than 1,000,000/mm ² , the adhesion of the separator may decrease, and if it exceeds 10,000,000/mm ² , the air permeability, ionic conductivity and resistance properties of the separator will be reduced. can

The separation membrane may satisfy one or more of the following conditions (i) to (vii), preferably, all of the conditions (i) to (vi). (i) air permeability 210-350 sec/100ml; (ii) Rs ≤ 110 mΩ (Rs is the resistance of the separator); (iii) less than 3.0% of longitudinal heat shrinkage at 150°C; (iv) 3.0% or less of transverse heat shrinkage at 150°C; (v) 0 mΩ < Rs - Ra ≤ 20 mΩ (Ra is the resistance of the porous substrate); (vi) 0 mΩ < Rb - Rs ≤ 10 mΩ (Rb is the resistance of the basement membrane); (vii) Electrode adhesion of 1.0 gf/mm or more.

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

Example 1

A first coating slurry was prepared by mixing a solid content containing 93 wt% of boehmite (AlOOH) having an average particle diameter of 500 nm and 7 wt% of an acrylonitrile copolymer and distilled water in a weight ratio of 23:77, respectively, and uniformly dispersing them. .

28.5% by weight of PVdF-HFP copolymer having an average particle diameter of 150 nm (containing 5% by weight of HPF), 66.5% by weight of an acrylic copolymer having an average particle diameter of 400nm, and 5% by weight of polyvinyl alcohol 5:95 A second coating slurry was prepared by mixing and uniformly dispersing in a weight ratio of .

The first coating slurry is roll-to-roll coated to a thickness of 3 μm on one surface of a polyethylene porous substrate (air permeability: 110 sec/100 ml) having a thickness of 9 μm, and then dried to a base membrane including a heat-resistant layer got

The second coating slurry was roll-to-roll coated on the heat-resistant layer to a thickness of 0.3 μm, and then dried to obtain a separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer.

Example 2

47.5% by weight of PVdF-HFP copolymer having an average particle diameter of 150 nm (containing 5% by weight of HPF), 47.5% by weight of an acrylic copolymer having an average particle diameter of 400nm, and 5% by weight of polyvinyl alcohol and distilled water were each mixed at 5:95 A separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1, except that the second coating slurry was prepared and applied by mixing and uniformly dispersing it in a weight ratio of .

Example 3

A solid content containing 66.5 wt% of a PVdF-HFP copolymer having an average particle diameter of 150 nm (containing 5 wt% of HPF), 28.5 wt% of an acrylic copolymer having an average particle diameter of 400 nm and 5 wt% of polyvinyl alcohol and distilled water were mixed at 5:95 A separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1, except that the second coating slurry was prepared and applied by mixing and uniformly dispersing it in a weight ratio of .

Comparative Example 1

A second coating slurry was prepared and applied by mixing and uniformly dispersing a solid content containing 95% by weight of an acrylic copolymer having an average particle diameter of 400nm and 5% by weight of polyvinyl alcohol and distilled water in a weight ratio of 5:95, respectively. In the same manner as in Example 1, a separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained.

Comparative Example 2

A solid content containing 95% by weight of a PVdF-HFP copolymer having an average particle diameter of 150nm (containing 5% by weight of HPF) and 5% by weight of polyvinyl alcohol and distilled water are mixed in a weight ratio of 5:95, respectively, and uniformly dispersed to the second A separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1, except that a coating slurry was prepared and applied.

Comparative Example 3

23.75% by weight of PVdF-HFP copolymer having an average particle diameter of 150 nm (containing 5% by weight of HPF), 71.25% by weight of an acrylic copolymer having an average particle diameter of 400nm, and 5% by weight of polyvinyl alcohol and distilled water were each mixed at 5:95 A separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1, except that the second coating slurry was prepared and applied by mixing and uniformly dispersing it in a weight ratio of .

Comparative Example 4

A solid content containing 71.25 wt% of a PVdF-HFP copolymer having an average particle diameter of 150 nm (containing 5 wt% of HPF), 23.75 wt% of an acrylic copolymer having an average particle diameter of 400 nm and 5 wt% of polyvinyl alcohol and distilled water were mixed at 5:95 A separation membrane sequentially including a porous substrate/heat-resistant layer/adhesive layer was obtained in the same manner as in Example 1, except that the second coating slurry was prepared and applied by mixing and uniformly dispersing it in a weight ratio of .

Experimental example

The test method for each of the physical properties measured in the present invention is as follows. Unless otherwise stated, the temperature was measured at room temperature (25° C.).

The plane and cross-section of the separators prepared according to the Examples and Comparative Examples were photographed by SEM and shown in FIG. 1, respectively, and the physical properties of the separators prepared according to the Examples and Comparative Examples were measured and the results are shown in Tables 1 to Table 3 shows.

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

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

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

-Electrode adhesion (gf/mm): After bonding the adhesive layer of the separator (MD direction 180mm * TD direction 25mm) and the electrode to face each other, insert it into the aluminum pouch, and press the aluminum pouch under the conditions of 80°C and 5MPa to create the separator and electrode was pressed. Thereafter, the adhesive force was measured while peeling the separator from the electrode using Shimatsu's UTM.

-Heat shrinkage (%): After placing a 200 × 200 mm separator specimen in an oven at 150° C. for 1 hour and leaving it in between A4 paper, it is cooled to room temperature and The contracted length was measured and the heat shrinkage rate was calculated using the following formula.

(Wherein, l ₃ is the transverse or longitudinal length of the specimen before shrinkage, and l ₄ is the transverse or longitudinal length of the specimen after shrinkage.)

Properties unit porous substrate basement membrane breathability seconds/100ml 153.6 181.1 resistance mΩ 83.6 100.2 MD heat shrinkage % 20 5 TD heat shrinkage % 20 5

Properties unit Example 1 Example 2 Example 3 Number of first organic particles (A) pcs/mm ² 29,000,000 35,000,000 44,000,000 Number of second organic particles (B) pcs/mm ² 4,000,000 3,200,000 2,300,000 B/A - 0.1379 0.0914 0.0523 breathability seconds/100ml 290.4 271.3 225.7 adhesion gf/mm 1.43 1.33 1.12 resistance mΩ 100.1 97.6 95.4 MD heat shrinkage % 3.0 2.5 2.5 TD heat shrinkage % 1.5 2.5 3.0

Properties unit Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Number of first organic particles (A) pcs/mm ² 0 52,000,000 25,000,000 50,000,000 Number of second organic particles (B) pcs/mm ² 4,300,000 0 5,400,000 1,900,000 B/A - - 0 0.216 0.0380 breathability seconds/100ml 301.2 200.1 310.5 195.7 adhesion gf/mm 1.84 1.00 1.92 1.04 resistance mΩ 125.0 84.9 105.3 93.2 MD heat shrinkage % 3.1 2.0 3.0 2.2 TD heat shrinkage % 1.5 2.5 2.0 3.3

The above description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains 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, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a dispersed form, and likewise 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 their equivalents should be construed as being included in the scope of the present invention.

Claims (10)

a base membrane including a porous substrate and a heat-resistant layer disposed on at least one surface of the porous substrate and including a plurality of inorganic particles bound by a binder; and
An adhesive layer comprising a plurality of first organic particles located on the surface of the heat-resistant layer and bound by a binder to form an electric conductive path and second organic particles having an average particle diameter larger than that of the first organic particles;
The ratio of the number of the second organic particles to the number of the first organic particles per unit area of the adhesive layer is 0.04 to 0.2,
A separation membrane satisfying all of the following conditions (i), (vi) and (vii):
(i) air permeability 210-350 sec/100ml;
(vi) 0mΩ < Rb - Rs ≤ 10 mΩ (Rb is the resistance of the base membrane, Rs is the resistance of the separator);
(vii) Electrode adhesion of 1.12 gf/mm or more. According to claim 1,
The number of the first organic particles is 10,000,000 ~ 100,000,000 / mm ² ,
The number of the second organic particles is 1,000,000 ~ 10,000,000 / mm ² of, the separation membrane. According to claim 1,
The ratio of the weight of the first organic particles to the total weight of the first and second organic particles is 0.3 to 0.7, the separation membrane. According to claim 1,
The porous substrate is a separator comprising 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. According to claim 1,
The content of the inorganic particles in the heat-resistant layer is 60 to 99% by weight,
The content of the first and second 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 ~ 5㎛,
The thickness of the adhesive layer is 0.5 ~ 1.5㎛, the separator. 7. The method of claim 6,
The ratio of the thickness of the adhesive layer to the thickness of the heat-resistant layer is 0.15 to 0.5, the separator. According to claim 1,
The first organic particles include a fluorine-based polymer having an average particle diameter of 50 to 300 nm,
The second organic particle is a separation membrane comprising an acrylic polymer having an average particle diameter of 350 to 1,000 nm. According to claim 1,
A separation membrane that satisfies one or more of the following conditions (ii) to (v):
(ii) Rs ≤ 110 mΩ (Rs is the resistance of the separator);
(iii) less than 3.0% of longitudinal heat shrinkage at 150°C;
(iv) 3.0% or less of transverse heat shrinkage at 150°C;
(v) 0 mΩ < Rs - Ra ≤ 20 mΩ (Ra is the resistance of the porous substrate). An electrochemical device comprising the separator according to any one of claims 1 to 9.

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