CN118830132A - Separator for electrochemical device comprising organic/inorganic composite porous coating and electrochemical device comprising the separator - Google Patents

Abstract

Provided is an electrochemical device separator including a porous polymer substrate and a porous organic/inorganic composite coating formed on at least one side of the porous polymer substrate. The porous organic/inorganic composite coating includes a granular binder polymer and inorganic particles. The granular binder polymer includes mixed polymer particles of a fluorine-based polymer and an acrylic acid-based polymer, and acrylic acid polymer particles. The porous organic/inorganic composite coating has a compositional morphology in a thickness direction having non-uniformity, wherein the content ratio of mixed polymer particles/acrylic acid polymer particles present on a surface portion opposite to a surface in contact with the porous polymer substrate is greater than the content ratio of mixed polymer particles/acrylic acid polymer particles present inside the porous organic/inorganic composite coating.

Description

Separator for electrochemical device comprising organic/inorganic composite porous coating and electrochemical device comprising the separator

Technical Field

This application claims the benefit of Korean Patent Application No. 10-2022-0054734, filed on May 3, 2022, and Korean Patent Application No. 10-2022-0061568, filed on May 19, 2022, respectively, which are hereby incorporated by reference in their entirety for all purposes.

The present disclosure relates to an electrochemical device separator improved in dry adhesion (adhesion in a dry state) and wet adhesion (adhesion in a state impregnated with an electrolyte).

Background Art

Electrochemical devices such as lithium secondary batteries are usually mainly composed of a positive electrode, a separator, a negative electrode and/or an electrolyte solution. Electrochemical devices are high-density energy storage devices that can be charged and discharged through reversible conversion between chemical energy and electrical energy, and are widely used in small electronic devices such as mobile phones and laptops. Recently, the application of electrochemical devices has rapidly expanded to hybrid electric vehicles (HEVs), plug-in electric vehicles (Plug-in EV), electric bicycles (e-bikes) and energy storage systems (ESS) to address environmental issues, high oil prices, energy efficiency and energy storage issues.

When manufacturing and using such lithium secondary batteries, ensuring the safety of lithium secondary batteries is an important task to be solved. In particular, separators commonly used in electrochemical devices exhibit extreme thermal shrinkage behavior at high temperatures or similar conditions due to their material properties and manufacturing process characteristics, resulting in internal short circuits. Recently, in order to ensure the stability of lithium secondary batteries, an organic/inorganic composite porous separator has been proposed, in which a porous organic/inorganic composite coating is formed by coating a porous polymer substrate with a mixture of inorganic particles and a binder resin. However, when an electrode assembly is formed by laminating electrodes and separators, there is a high risk of separation of electrodes and separators due to insufficient adhesion, in which case the inorganic particles de-embedded during the separation process may become local defects in the device. Therefore, a separator in which an acrylic polymer adhesive is applied to a porous organic/inorganic composite coating to improve the adhesion between the electrode and the separator has been proposed. When an acrylic polymer adhesive is used, dry adhesion is improved, but there is a problem that wet adhesion is reduced due to problems such as swelling or dissolution of the acrylic polymer adhesive by the electrolyte after being applied to the battery.

Therefore, there is a need to develop a separator that can maintain high adhesion from the time of manufacturing the separator including the porous organic/inorganic composite coating layer to during the use of the battery.

Summary of the invention

Technical issues

An object of the present disclosure is to provide an organic/inorganic composite porous separator having improved bonding strength with electrodes in both dry and wet states.

Furthermore, another object of the present disclosure is to provide a separator in which inorganic particles are not desorbed from the porous organic/inorganic composite coating layer, and high durability and dielectric properties are maintained.

Other purposes and advantages of the present disclosure will be understood from the following description.On the other hand, it is easy to understand that the purposes and advantages of the present disclosure can be achieved by the means or methods described in the claims and their combinations.

Technical Solution

A first aspect of the present disclosure relates to a separator for an electrochemical device, the separator comprising a porous polymer substrate and a porous organic/inorganic composite coating formed on at least one side of the porous polymer substrate.

The porous organic/inorganic composite coating comprises a particulate binder polymer and inorganic particles.

The particulate binder polymer includes mixed polymer particles of fluorine-based polymer and acrylic-based polymer, and acrylic polymer particles,

wherein the acrylic-based polymer included in the hybrid polymer particles does not include styrene repeating units, and the acrylic-based polymer included in the acrylic polymer particles includes styrene repeating units,

The porous organic/inorganic composite coating has heterogeneity in its composition morphology in the thickness direction, wherein a content ratio of mixed polymer particles/acrylic polymer particles present on a surface portion opposite to a surface in contact with the porous polymer substrate is greater than a content ratio of mixed polymer particles/acrylic polymer particles present in an interior of the porous organic/inorganic composite coating.

A second aspect of the present disclosure is that, in the first aspect, the porous organic/inorganic composite coating has a heterogeneity in composition morphology in the thickness direction, wherein the content of mixed polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content of mixed polymer particles present in the interior of the porous organic/inorganic composite coating.

A third aspect of the present disclosure is that, in the second aspect, the porous organic/inorganic composite coating has a heterogeneity in composition morphology in the thickness direction, wherein the content of acrylic polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content of acrylic polymer particles present in the interior of the porous organic/inorganic composite coating.

A fourth aspect of the present disclosure resides in that, in any one of the first to third aspects, the average particle diameter (D50) of the hybrid polymer particles is smaller than the average particle diameter (D50) of the acrylic polymer particles.

The fifth aspect of the present disclosure is that in the fourth aspect, the average particle size (D50) of the hybrid polymer particles is in the range of 100nm to 500nm, and the average particle size (D50) of the acrylic polymer particles is in the range of 200nm to 700nm. More specifically, the average particle size (D50) of the hybrid polymer particles is in the range of 200nm to 400nm, and the average particle size (D50) of the acrylic polymer particles is in the range of 300nm to 500nm.

A sixth aspect of the present disclosure resides in that, in any one of the first to fifth aspects, a mixing weight ratio of the hybrid polymer particles and the acrylic polymer particles is 8:2 to 2:8.

A seventh aspect of the present disclosure resides in that, in any one of the first to sixth aspects, the glass transition temperature Tg of the acrylic-based polymer included in the hybrid polymer particles is lower than the glass transition temperature Tg of the acrylic-based polymer included in the acrylic polymer particles by more than 10° C. More specifically, the glass transition temperature Tg of the acrylic-based polymer included in the hybrid polymer particles is 10° C. to 30° C., and the glass transition temperature Tg of the acrylic-based polymer included in the acrylic polymer particles is 30° C. to 50° C.

An eighth aspect of the present disclosure resides in that, in any one of the first to seventh aspects, the fluorine-based polymer is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and other polymerizable monomers, or a mixture of two or more thereof.

The ninth aspect of the present disclosure is that in any one of the first to eighth aspects, the polymerizable monomer includes at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene and fluorinated vinyl.

A tenth aspect of the present disclosure resides in that, in any one of the first to ninth aspects, the fluorine-based polymer is a copolymer of vinylidene fluoride and hexafluoropropylene.

An eleventh aspect of the present disclosure resides in that, in any one of the first to tenth aspects, the content of the polymerizable monomer is 1 to 20 weight % of the copolymer.

The twelfth aspect of the present disclosure is that, in any one of the first to eleventh aspects, the acrylic-based polymer constituting the hybrid polymer particles and the acrylic-based polymer constituting the acrylic polymer particles each independently include an alkyl (meth)acrylate repeating unit having an alkyl group with 1 to 18 carbon atoms.

A thirteenth aspect of the present disclosure resides in that, in any one of the first to twelfth aspects, the porous organic/inorganic composite coating includes a particulate binder polymer in an amount of 1 wt % to 30 wt % of the porous inorganic/organic composite coating.

A fourteenth aspect of the present disclosure resides in that, in any one of the first to thirteenth aspects, an average particle diameter (D50) of the inorganic particles is within a range of 200 nm to 3 μm.

The fifteenth aspect of the present disclosure is that in any one of the first to fourteenth aspects, the porous organic/inorganic composite coating is formed by coating and drying a slurry in which a particulate binder polymer and inorganic particles are dispersed in an aqueous dispersion medium on at least one surface of a porous polymer substrate.

A sixteenth aspect of the present disclosure is directed to an electrochemical device, wherein the electrochemical device includes a negative electrode, a positive electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator according to any one of the first to fourteenth aspects.

A seventeenth aspect of the present disclosure resides in that, in the sixteenth aspect, the electrochemical device is a lithium secondary battery.

Beneficial Effects

The porous organic/inorganic composite coating of the separator according to the present disclosure includes mixed polymer particles of fluorine-based polymers and acrylic-based polymers, and acrylic polymer particles. At the same time, the composition morphology of the porous organic/inorganic composite coating in the thickness direction has heterogeneity, wherein the content ratio of the mixed polymer particles/acrylic polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content ratio of the mixed polymer particles/acrylic polymer particles present in the interior of the porous organic/inorganic composite coating.

According to the present disclosure, the content ratio of the mixed polymer particles/acrylic polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content ratio of the mixed polymer particles/acrylic polymer particles present inside the porous organic/inorganic composite coating. Since the fluorine-based polymer included in the mixed polymer particles is insoluble in the electrolyte, even if the mixed polymer particles are immersed in the electrolyte, even if the acrylic-based polymer is included at the same time, the mixed polymer particles will maintain their shape. Therefore, even in a wet state, the separator of the present disclosure can maintain adhesion to the electrode without significantly losing adhesion to the electrode. On the other hand, the acrylic polymer particles also help to maintain the adhesion of the separator to the electrode in a dry state.

Therefore, in the roll-to-roll continuous process of manufacturing an electrode assembly by laminating electrodes and the separator of the present disclosure, the shape stability and workability of the electrode assembly are improved. In addition, since the battery is manufactured using the electrode assembly including the separator, even if the battery is impregnated with an electrolyte, a high bonding force can be maintained between the separator and the electrode, and the interface resistance characteristics will not deteriorate. In addition, since the binder resin particles maintain high adhesion in both dry and wet states, the inorganic particles included in the porous organic/inorganic composite coating will not desorb and are well fixed, so that the shape stability of the separator can be improved. Therefore, it has the effect of improving the thermal stability and dielectric properties of the battery.

Furthermore, in the case where the acrylic-based polymer included in the hybrid polymer particles does not include a styrene repeating unit and the acrylic-based polymer included in the acrylic polymer particles includes a styrene repeating unit, adhesion between the porous polymer substrate and the porous organic/inorganic composite coating layer increases.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings show preferred embodiments of the present disclosure and explain the principles of the present disclosure together with the detailed description, but the scope of the present disclosure is not limited thereto. On the other hand, the shapes, sizes, proportions or ratios of the elements in the accompanying drawings included in this specification may be exaggerated to emphasize a clearer description.

FIG. 1 is a schematic diagram showing a cross section of a separator according to a specific embodiment of the present disclosure;

FIG. 2 a shows a SEM image of the surface of the separator of Example 1 before electrolyte impregnation, and FIG. 2 b is a partial enlarged view of FIG. 2 a ;

FIG3a shows a SEM image of the surface of the separator of Comparative Example 1, and FIG3b is a partial enlarged view of FIG3b;

FIG4 is a SEM image of a cross section of the separator of Example 1; and

FIG. 5 is an EDS image of a cross section of the separator of Example 1. FIG.

[reference numerals]

1: Porous polymer substrate

3: Porous organic/inorganic composite coating

5: Mixed polymer particles

7: Acrylic polymer particles

9: Inorganic particles

10: Partition

DETAILED DESCRIPTION

The terms or words used in the specification and claims should not be interpreted as conventional meanings or dictionary meanings, but should be interpreted as meanings and concepts consistent with the technical concept of the present invention based on the principle that the inventor can appropriately define the concept of the term to describe his invention in the best way. Therefore, since the configurations described in the embodiments described herein are only the most preferred embodiments of the present disclosure and do not represent the entire technical concept of the present disclosure, it should be understood that various equivalents and modifications that can replace them may exist at the time of this application.

FIG. 1 is a schematic diagram showing a cross section of a separator 10 for an electrochemical device according to a specific embodiment of the present disclosure.

In the present disclosure, the separator 10 includes a porous polymer substrate 1 and a porous organic/inorganic composite coating 3 formed on at least one side of the porous polymer substrate. Although FIG. 1 shows that the porous organic/inorganic composite coating 3 is formed only on one side surface of the porous polymer substrate 1, the porous organic/inorganic composite coating 3 may also be formed on the other side surface of the porous polymer substrate 1.

The porous organic/inorganic composite coating 3 includes a particulate binder polymer (5 and 7) and inorganic particles 9. The particulate binder polymer (5 and 7) includes hybrid polymer particles 5 of a fluorine-based polymer and an acrylic-based polymer, and acrylic polymer particles 7.

In the present disclosure, the acrylic-based polymer included in the hybrid polymer particles does not include styrene repeating units, and the acrylic-based polymer included in the acrylic polymer particles includes styrene repeating units. Specifically, the expression "does not include styrene repeating units" means that in the process of polymerizing the acrylic-based polymer included in the hybrid polymer particles or polymerizing the acrylic-based resin included in the acrylic polymer particles, a styrene compound as a monomer, a copolymer including styrene repeating units, or a polymer including styrene repeating units is not included.

As shown in Figure 1, the composition morphology of the porous organic/inorganic composite coating 3 in the thickness direction has heterogeneity, wherein the content ratio of the mixed polymer particles 5/acrylic polymer particles 7 present on the surface portion opposite to the surface in contact with the porous polymer substrate 1 is greater than the content ratio of the mixed polymer particles 5/acrylic polymer particles 7 present in the interior of the porous organic/inorganic composite coating.

In the specification of the present disclosure, "heterogeneity of composition morphology in the thickness direction, wherein the content ratio of mixed polymer particles/acrylic polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content ratio of mixed polymer particles/acrylic polymer particles present in the interior of the porous organic/inorganic composite coating", wherein, if the content ratio of mixed polymer particles/acrylic polymer particles present on the surface portion of the porous organic/inorganic composite coating opposite to the surface in contact with the porous polymer substrate is greater than the content ratio of mixed polymer particles/acrylic polymer particles present below (inside) the surface portion of the porous organic/inorganic composite coating, it should be interpreted as including any aspect. For example, it should be interpreted as including all of the following meanings: a porous organic/inorganic composite coating formed such that the content ratio of the mixed polymer particles/acrylic polymer particles decreases linearly from the surface of the porous organic/inorganic composite coating to the porous polymer substrate; a porous organic/inorganic composite coating formed such that the content ratio of the mixed polymer particles/acrylic polymer particles decreases non-linearly from the surface of the porous organic/inorganic composite coating to the porous polymer substrate; and a porous organic/inorganic composite coating formed such that the content ratio of the mixed polymer particles/acrylic polymer particles decreases discontinuously from the surface of the porous organic/inorganic composite coating to the porous polymer substrate, and the like.

Therefore, the content ratio of the mixed polymer particles/acrylic polymer particles present on the surface portion opposite to the surface of the porous organic/inorganic composite coating in contact with the porous polymer substrate is greater than the content ratio of the mixed polymer particles/acrylic polymer particles present inside the porous organic/inorganic composite coating. Since the fluorine-based polymer included in the mixed polymer particles is insoluble in the electrolyte, even if the mixed polymer particles are immersed in the electrolyte, even if the acrylic-based polymer is included at the same time, the mixed polymer particles will maintain their shape. Therefore, even in a wet state, the separator of the present disclosure can maintain adhesion to the electrode without significantly losing adhesion to the electrode. On the other hand, the acrylic polymer particles also help to maintain the adhesion of the separator to the electrode in a dry state.

The porous organic/inorganic composite coating 3 may have a composition morphology heterogeneity in the thickness direction, wherein the content of the mixed polymer particles 5 present on the surface portion opposite to the surface in contact with the porous polymer substrate 1 is greater than the content of the mixed polymer particles 5 present inside the porous organic/inorganic composite coating. In addition, the porous organic/inorganic composite coating 3 may have a composition morphology heterogeneity in the thickness direction, wherein the content of the acrylic polymer particles 7 present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content of the acrylic polymer particles 7 present inside the porous organic/inorganic composite coating 3.

Therefore, when the mixed polymer particles 5 and/or the acrylic polymer particles 7 have the heterogeneity of the composition morphology of the above-mentioned form in the thickness direction, the mixed polymer particles 5 and the acrylic polymer particles 7 are more present on the surface portion opposite to the surface in contact with the porous polymer substrate 1, rather than being present in the interior of the porous organic/inorganic composite coating 3. Therefore, since the adhesion characteristics of the polymer particles present on the surface are large, the dry/wet adhesion to the electrode is increased. In addition, the resistance to external stimuli such as peeling and scratching is increased, and the lamination characteristics of the electrode are improved. Therefore, very excellent characteristics can be exhibited in battery assembly processes such as winding and lamination. In addition, since the inorganic particles increase toward the inside, the porosity is improved, and therefore excellent ionic conductivity characteristics can be exhibited, thereby contributing to the improvement of battery performance.

According to a specific embodiment of the present disclosure, the porous polymer substrate 1 can provide a migration path for lithium ions while preventing short circuits by electrically insulating the negative electrode and the positive electrode, and can be used without particular limitation as long as it is a porous polymer substrate generally used as a separator of an electrochemical device. As an example of a substrate for a separator, for example, a porous polymer film or nonwoven fabric including at least one polymer resin of a polyolefin such as polyethylene, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and polyethylene naphthalate can be used.

In the present disclosure, the thickness of the porous polymer substrate may be 3 μm to 50 μm. Although the range of the substrate for the separator is not particularly limited to the above range, if the thickness is too thin, exceeding the above lower limit, the mechanical properties are reduced, and the separator may be easily damaged during the use of the battery. At the same time, the pore size and porosity present in the substrate for the separator are also not particularly limited, but may be 0.01 μm to 50 μm and 10% to 95% by volume, respectively.

The porous organic/inorganic composite coating 3 can be prepared by mixing a plurality of inorganic particles 9 and a particulate binder polymer (5 and 7). Since the porous polymer substrate 1 is coated with the porous organic/inorganic composite coating 3 including the inorganic particles 9, the heat resistance and mechanical properties of the separator 10 can be further improved. According to a preferred embodiment of the present disclosure, the porous organic/inorganic composite coating 3 is disposed on both sides of the porous polymer substrate 1. As described above, by forming the porous organic/inorganic composite coating 3 on both sides of the porous polymer substrate 1, both the wet adhesion and the dry adhesion between the positive electrode and the separator and between the negative electrode and the separator can be improved.

The porous organic/inorganic composite coating 3 may have a microporous structure due to the interstitial volume between the constituent inorganic particles 9 and the particulate binder polymer (5 and 7). The inorganic particles 9 serve as a spacer capable of maintaining the physical shape of the porous organic/inorganic composite coating 3. The interstitial volume refers to the space limited by the substantial surface contact with the inorganic particles 9 and the particles of the particulate binder polymer (5 and 7). In addition, since the inorganic particles 9 generally have the property that their physical properties will not change even at a high temperature of 200°C or higher, the separator 10 has excellent heat resistance through the porous organic/inorganic composite coating 3. In the present disclosure, based on the thickness formed on either side of the porous polymer substrate 1, the thickness of the porous organic/inorganic composite coating 3 may be in the range of 1 μm to 50 μm, 2 μm to 30 μm, or 2 μm to 20 μm.

In the present disclosure, when forming the porous organic/inorganic composite coating 3, the particulate binder polymer (5 and 7) is added to the dispersion medium in the form of particles for coating and drying so as to maintain the particle shape, and therefore the particulate binder polymer is different from the non-particulate binder polymer which is coated and dried in a solvent-dissolved state.

In an embodiment of the present disclosure, the particulate binder polymer (5 and 7) may be present in an amount of about 90% by weight or more, or about 99% by weight or more, based on the binder component present in the porous organic/inorganic composite coating 3. In this specification, the particulate binder polymer (5 and 7) may be referred to as polymer particles, resin particles, or binder particles. The particulate binder polymer (5 and 7) forms a porous organic/inorganic composite coating 3 having a layered structure by adhesion between the inorganic particles 9 and mutual adhesion between the inorganic particles 9 and the porous polymer substrate 1.

In the present disclosure, the average particle size (D50) of the hybrid polymer particles may be smaller than the average particle size (D50) of the acrylic polymer particles. By making the average particle size (D50) of the hybrid polymer particles smaller than the average particle size (D50) of the acrylic polymer particles, a porous organic/inorganic composite coating having heterogeneity in composition morphology in the thickness direction may be more easily formed.

In an embodiment of the present disclosure, the average particle size (D50) of the mixed polymer particles is 100nm to 500nm, and the average particle size (D50) of the acrylic polymer particles is 200nm to 700nm. More specifically, the average particle size (D50) of the mixed polymer particles can be 200nm to 400nm, and the average particle size (D50) of the acrylic polymer particles can be 300nm to 500nm. In addition, the mixing weight ratio of the mixed polymer particles and the acrylic polymer particles can be 8:2 to 2:8.

Hybrid polymer particles can be prepared with reference to, for example, WO 2020/263936, and can be combined with the references in the present disclosure.

The fluorine-based polymer included in the hybrid polymer particles, which is insoluble in the electrolyte, may be a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and other polymerizable monomers, or a mixture of two or more thereof.

Other polymerizable monomers may include at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene and fluorinated vinyl, but are not limited thereto. In particular, the fluorine-based polymer may be a copolymer of vinylidene fluoride and hexafluoropropylene. The content of vinylidene fluoride and other polymerizable monomers may be 1% to 20% by weight of the copolymer, but are not limited thereto.

In the present disclosure, the content of comonomer in PVDF-based polymer can be measured by 1H-NMR method using Varian 500MHz. For detailed measurement methods, please refer to Journal of Materials Chemistry, 2012, 22, 341 or AMT-3412-0k. In order to confirm the NMR spectrum, suitable equipment such as Bruker Avance III HD 700MHz NMR or Varian 500MHz NMR can be used.

The acrylic acid-based polymer constituting the hybrid polymer particles and the acrylic acid-based polymer constituting the acrylic polymer particles may each independently include an alkyl (meth) acrylate repeating unit having an alkyl group having 1 to 18 carbon atoms, but is not limited thereto. However, the acrylic acid-based polymer included in the hybrid polymer particles does not include a styrene repeating unit, and the acrylic acid-based polymer included in the acrylic polymer particles includes a styrene repeating unit.

In an embodiment of the present disclosure, the Tg of the acrylic-based polymer included in the hybrid polymer particles may be lower than the Tg of the acrylic-based polymer included in the acrylic polymer particles by more than 10° C. Since the lower the Tg of the acrylic-based polymer, the better the adhesion, the lower the Tg of the acrylic-based polymer included in the hybrid polymer particles, the higher the dry/wet adhesion of the hybrid polymer particles to the electrode.

More specifically, the Tg of the acrylic-based polymer included in the hybrid polymer particles may be 10° C. to 30° C., and the Tg of the acrylic-based polymer included in the acrylic polymer particles may be 30° C. to 50° C. Although the acrylic-based polymer included in the hybrid polymer particles has a lower Tg, the particle shape can be maintained even at room temperature due to the mixing of the fluorine-based polymer. In addition, when the Tg of the acrylic-based polymer included in the acrylic polymer particles is selected to be higher than or equal to room temperature, the particle shape can be maintained at room temperature, thereby exhibiting electrode adhesion during lamination with an electrode.

The glass transition temperature (Tg) of the acrylic-based polymer may be 40° C. or less.

More specifically, the acrylic-based polymer is a polymer having carboxylic acid ester as a repeating unit, and may preferably be (meth)acrylic acid ester. Specific examples of such (meth)acrylates may include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, ethylene di(meth)acrylate, and the like, and may be at least one selected from them. Among these polymers, at least one selected from methyl (meth)acrylate, ethyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate is preferred, and methyl (meth)acrylate is particularly preferred.

The porous organic/inorganic composite coating layer may include the particulate binder resin in an amount of 1 wt % to 30 wt % of the porous organic/organic composite coating layer, but is not limited thereto.

The inorganic particles included in the porous organic/inorganic composite coating are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles are not particularly limited as long as no oxidation and/or reduction reaction occurs within the operating voltage range of the applied electrochemical device (e.g., 0 to 5V based on Li/Li+). In particular, when using inorganic particles with ion transport capability, performance can be improved by improving the ionic conductivity in the electrochemical device. In addition, when using inorganic particles with a high dielectric constant as the inorganic particles, the ionic conductivity of the electrolyte can be improved by helping to increase the degree of dissociation of electrolyte salts such as lithium salts in liquid electrolytes.

Based on the above reasons, the inorganic particles may include inorganic particles having a high dielectric constant of 5 or more or 10 or more, inorganic particles having lithium ion transporting ability, or mixtures thereof. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include: BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _1-x La _x Zr _1-y Ti _y O ₃ (PLZT, wherein 0<x<1, 0<y<1), Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), hafnium dioxide (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO ₂ , etc., alone or as a mixture of two or more. Furthermore, when the above-mentioned high dielectric constant inorganic particles are mixed with inorganic particles having lithium ion transporting ability, their synergistic effect can be doubled.

Non-limiting examples of inorganic particles having lithium ion transport capability include lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , 0<x<2, 0<y<3), lithium aluminum titanium phosphate ((Li _x Al _y Ti _z )(PO ₄ ) ₃ , 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) _x O _y based glass (0<x<4, 0<y<13) such as 14Li ₂ O-9Al ₂ O ₃ -38TiO ₂ -39P ₂ O _{5 )} , lithium lanthanum titanate (Li _x La _y TiO ₃ , 0<x<2, 0<y<3), lithium germanium thiophosphate (Li x Ge y P z S w 4 , 0<x<2, 0<y<3), and lithium thiophosphate (Li _x Ge _y P _z S _{w 4} , 0<_{x< 4 ,} 0<y<13). , 0<x<4, 0<y<1, 0<z<1, 0<w< ₅ ), _lithium nitride such as _Li3N ( _LixNy , 0<x<4, 0<y< _{2 )} , _SiS2 -based glass ( _LixSiySz , 0 _< x _{< 3} , 0<y<2, 0<z<4) such as Li3PO4- _Li2S - _SiS2 , _P2S5 -based glass ( _{LixPySz ,} 0<x< ₃ , 0<y<3, 0<z<7) such as _LiI - _Li2SP2S5 , or mixtures thereof.

In the porous organic/inorganic composite coating, the content ratio of the inorganic particles is determined by considering the thickness, pore size and porosity of the porous organic/inorganic composite coating finally obtained, but based on the weight ratio, the inorganic particles can be included in the range of 70 wt % to 99 wt % based on 100 wt % of the porous organic/inorganic composite coating. When the content of the inorganic particles is less than 70 wt %, the heat resistance may be reduced. On the other hand, when the content of the inorganic particles is too large, the amount of the binder is relatively too small, so the adhesion of the porous organic/inorganic composite coating may be reduced.

According to a specific embodiment of the present disclosure, the inorganic particle size of the porous organic/inorganic composite coating is not limited, but can be as far as possible in the range of 0.001 μm to 10 μm, so as to form a coating with uniform thickness and appropriate porosity. For example, within the above range, the inorganic particle size is in the range of 200nm to 3 μm, 200nm to 2 μm, or 200nm to 1 μm. When the inorganic particle size meets this range, the dispersibility is maintained, so it is easy to control the physical properties of the separator, and the increase in the thickness of the porous organic/inorganic composite coating can be avoided, thereby improving the mechanical properties. In addition, due to the large pore size, the probability of internal short circuit during battery charging and discharging is low.

On the other hand, in an embodiment of the present disclosure, a separator including a porous organic/inorganic composite coating can be prepared by mixing binder particles and inorganic particles with an aqueous dispersion medium to prepare a slurry for forming a coating, and then coating the slurry on at least one side surface of a porous polymer substrate.

As the coating method, dip coating, die coating, roll coating, comma coating, or a combination of the above methods can be used.

In an embodiment of the present disclosure, the aqueous dispersion medium may include at least one of water and an alcohol having 1 to 5 carbon atoms. For example, the aqueous dispersion medium may include a mixture of water and isopropanol. By using an aqueous dispersion medium in the above production method, the binder particles are dispersed while maintaining a particle shape in the aqueous dispersion medium, and will not dissolve in the dispersion medium. Therefore, the binder particles can maintain a particle state in the prepared porous organic/inorganic composite coating, and will not enter the pores of the porous polymer substrate.

On the other hand, in the embodiment of the present disclosure, the slurry used to form the coating is preferably controlled so that the concentration of the solid (excluding the dispersion medium) is in the range of 20 wt % to 50 wt %. Advantageously, the separator containing the porous organic/inorganic composite coating having a non-uniform composition morphology of the present disclosure is obtained by controlling the concentration, average particle size and content ratio of the solid of the injected binder particles within the above range.

On the other hand, the separator of the present disclosure can be applied to an electrochemical device. The electrochemical device may include a negative electrode and a positive electrode, and the separator may be inserted between the negative electrode and the positive electrode. The electrochemical device includes all devices for performing electrochemical reactions, and specific examples thereof include various primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, in secondary batteries, lithium ion secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferred.

In a specific embodiment according to the present disclosure, the electrochemical device can be manufactured according to conventional methods known in the art. According to an embodiment of the present disclosure, the electrochemical device can be configured by inserting the above-mentioned separator between the positive electrode and the negative electrode. In addition, the electrode assembly can be assembled by laminating the negative electrode, the separator and the positive electrode in a battery case, and the electrochemical device can be manufactured by loading the electrode assembly and then injecting the electrolyte.

In the embodiments of the present disclosure, the electrode is not particularly limited, and the electrode active material can be prepared in the form of adhering to the electrode collector according to conventional methods known in the art. As a non-limiting example of the positive electrode active material in the electrode active material, a conventional positive electrode active material that can be used for the positive electrode of a conventional electrochemical device can be used, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium intercalation material (lithium intercalation material) such as a composite oxide formed by a combination of the above materials is preferred. As a non-limiting example of the negative electrode active material, a conventional negative electrode active material that can be used for the negative electrode of a conventional electrochemical device can be used, and in particular, lithium metal or lithium alloy, such as carbon, petroleum coke, activated carbon, graphite or other carbon lithium adsorption materials are preferred. Non-limiting examples of positive electrode collectors include foils made of aluminum, nickel or a combination thereof, and non-limiting examples of negative electrode collectors include foils made of copper, gold, nickel, or copper alloys or a combination of the above materials.

The electrolyte that can be used in the present disclosure is a salt having the same structure as A ⁺ B ⁻ , A ⁺ includes ions formed of alkali metal cations such as Li ⁺ , Na ⁺ , K ⁺ , or a combination thereof, or B ⁻ includes PF ₆ ⁻ , BF ₄ ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , CH ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , N(CF ₃ SO ₂ ) ₂ ⁻ , C(CF ₂ SO ₂ ) ₃ ⁻ , or a combination thereof. In the electrolyte, the salt can be dissolved or dissociated in an organic solvent or an organic solvent consisting of a mixture thereof, wherein the organic solvent includes propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), and gamma-butyrolactone (γ-butyrolactone), but is not limited thereto.

The injection of electrolyte can be carried out at an appropriate stage of the battery manufacturing process according to the manufacturing process and the physical properties required by the final product. That is, it can be applied before assembling the battery or in the final stage of assembling the battery. As a process for applying the electrode assembly of the present disclosure to the battery, in addition to the usual winding process, lamination, stacking and folding processes of the separator and the electrode are also possible.

Embodiments of the invention

Hereinafter, examples will be given to describe the present disclosure in detail. However, embodiments according to the present disclosure may be modified in various other forms, and the scope of the present disclosure should not be interpreted as being limited to the embodiments described below. The embodiments of the present disclosure are provided to more completely explain the present disclosure to those of ordinary skill in the art.

Example

Example 1

8.2 parts by weight of hybrid polymer particles [Arkema, LBG4330LX, D50: 300 nm, a copolymer obtained by polymerizing VDF and HFP at a molar ratio of 95:5 and a copolymer of ethyl acrylate and methyl methacrylate (Tg 20°C) mixed at a weight ratio of 7:3], 8.2 parts by weight of acrylic polymer particles [LGC, AD-S11, D50: 400 nm, a copolymer of styrene and butyl acrylate (Tg 40°C)], and 80 parts by weight of inorganic particles ( _Al2O3 , _D50 : 500 nm) were added to water and dispersed to prepare a dispersion liquid (solid concentration of 35 wt%) for forming a porous coating layer.

Then, a polyethylene material substrate (porosity 40%, thickness 9 μm) for the separator was prepared, the dispersion was applied to both sides of the substrate by a scraper by a rod coating method, and then dried with hot air at 50°C using a hot air gun to form a porous coating having a thickness of 12 μm (based on the thickness of one side).

FIG4 is a SEM image of a cross section of the separator according to Example 1, and FIG5 is an EDS image of a cross section of the separator according to Example 1. Referring to FIG5, by analyzing the distribution of the F element contained in the mixed polymer particles, the distribution of the mixed polymer particles included in the porous organic/inorganic composite coating can be confirmed from the image of F Kα1,2. At the same time, the distribution of the acrylic polymer particles can be confirmed from the image of RuLα1, wherein the distribution of the Ru element is analyzed after staining with RuO ₄ .

Example 2

A porous coating layer was formed in the same manner as in Example 1, except that the content of the mixed polymer particles was 10.2 parts by weight, the content of the acrylic polymer particles was 10.2 parts by weight, and the content of the inorganic particles was changed to 75 parts by weight to prepare a dispersion (35 wt %) for forming a porous coating layer.

Comparative Example 1

A porous coating layer was formed in the same manner as in Example 1 except that a dispersion liquid (solid concentration: 35 wt %) for forming a porous coating layer was prepared by changing the content of acrylic polymer particles to 16.4 parts by weight without adding mixed polymer particles.

Comparative Example 2

A porous coating layer was formed in the same manner as in Example 1 except that a dispersion liquid (solid concentration: 35 wt %) for forming a porous coating layer was prepared by changing the content of the mixed polymer particles to 16.4 parts by weight without adding acrylic polymer particles.

Comparative Example 3

A porous coating layer was formed in the same manner as in Example 1, except that a dispersion liquid (solid concentration: 35 wt %) for forming a porous coating layer was prepared by changing the copolymer of ethyl acrylate and methyl methacrylate in the mixed polymer particles to a copolymer of styrene and butyl methacrylate.

Comparative Example 4

A porous coating layer was formed in the same manner as in Example 1, except that a dispersion liquid (solid concentration: 35 wt %) for forming the porous coating layer was prepared by changing the copolymer of styrene and butyl acrylate in the acrylic polymer particles to a polymer of butyl acrylate.

Comparative Example 5

A porous coating layer was formed in the same manner as in Example 1, except that a dispersion (solid concentration of 35 wt %) was prepared for forming the porous coating layer by changing the copolymer of ethyl acrylate and methyl methacrylate in the mixed polymer particles to a copolymer of styrene and butyl methacrylate, and by changing the copolymer of styrene and butyl acrylate in the acrylic polymer particles to a polymer of butyl acrylate.

Measurement of average particle size D50

D50 may be defined as the particle size based on 50% particle size distribution, and is measured using a laser diffraction method.

Measurement of Tg

The Tg of 25 mg of the sample was measured using DSC in a nitrogen atmosphere at a temperature increase rate of 10°C/min over a range from room temperature to 300°C.

Wet Adhesion Test Sample Preparation

The separator obtained in each of the examples and comparative examples was laminated with the positive electrode, immersed in 1.0 g of electrolyte (ethylene carbonate: ethyl methyl carbonate content ratio = 7:3, LiPF ₆ 1M), and left at room temperature for 24 hours. Thereafter, a sample was prepared by laminating using hot pressing. At this time, pressurization was performed at 70°C and 5 kgf for 5 minutes. The size of the sample was 2 cm×6 cm.

The positive electrode was prepared by mixing LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , PVdF and carbon black at a weight ratio of 97.0:1.5:1.5 and dispersing them in 2-methyl-2-pyrrolidone to prepare a positive electrode slurry, coating it on an aluminum current collector, and then drying and rolling to prepare a positive electrode.

Dry Adhesion Test Specimen Preparation

The separator obtained in each of the examples and comparative examples was laminated with the negative electrode using hot pressing to prepare a sample. At this time, pressing was performed at 60° C. and 6.5 MPa for 1 second. The size of the sample was 2 cm×6 cm.

The negative electrode was prepared by mixing graphite, SBR and CMC at a weight ratio of 89.2:10:0.8 and dispersing them in distilled water to prepare a negative electrode slurry, coating the slurry on a copper current collector, drying and rolling the slurry to prepare a negative electrode.

Measurement of adhesion to electrodes

Each of the samples prepared above was used to evaluate the wet adhesion and dry adhesion of the separator, and the results are summarized in the following Table 1. After each sample was prepared, the adhesion was measured after the sample was left at room temperature for 1 hour. The adhesion was measured by peeling at an angle of 180° for dry and 90° for wet using a tensile tester (UTM equipment).

[Table 1]

As can be seen from Table 1, the separator according to the present disclosure has been confirmed to have good wet adhesion and dry adhesion with the electrode. In the case of Comparative Example 1, the dry adhesion is high, but the wet adhesion is low, so when applied to an actual battery, the battery performance may deteriorate. The problem with Comparative Example 2 is that since the dry adhesion is low, the adhesion is reduced during the electrode assembly manufacturing process. In addition, in the case of Comparative Examples 3 to 5, because the wet adhesion and the dry adhesion are all low, the adhesion is reduced during the electrode assembly manufacturing process, and the battery performance may deteriorate when a real battery is applied. However, the separator according to each embodiment exhibits a high level of wet adhesion and dry adhesion, thereby exhibiting excellent electrochemical effects during the electrode assembly manufacturing process and battery operation.

Claims (18)

1. A separator for an electrochemical device, the separator comprising a porous polymer substrate and a porous organic/inorganic composite coating formed on at least one side of the porous polymer substrate, wherein the porous organic/inorganic composite coating comprises a particulate binder polymer and inorganic particles, The particulate binder polymer includes hybrid polymer particles of a fluorine-based polymer and an acrylic-based polymer, and acrylic polymer particles, and The acrylic-based polymer included in the hybrid polymer particles does not include styrene repeating units, and the acrylic-based polymer included in the acrylic polymer particles includes styrene repeating units, The porous organic/inorganic composite coating has heterogeneity in composition morphology in a thickness direction, wherein a content ratio of mixed polymer particles/acrylic polymer particles present on a surface portion opposite to a surface in contact with the porous polymer substrate is greater than a content ratio of mixed polymer particles/acrylic polymer particles present in an interior of the porous organic/inorganic composite coating. 2. The separator according to claim 1, wherein the composition morphology of the porous organic/inorganic composite coating in the thickness direction has heterogeneity, wherein the content of mixed polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content of mixed polymer particles present in the interior of the porous organic/inorganic composite coating. 3. The separator according to claim 1, wherein the composition morphology of the porous organic/inorganic composite coating has heterogeneity in the thickness direction, wherein the content of acrylic polymer particles present on the surface portion opposite to the surface in contact with the porous polymer substrate is greater than the content of acrylic polymer particles present in the interior of the porous organic/inorganic composite coating. 4 . The separator according to claim 1 , wherein an average particle size (D50) of the hybrid polymer particles is smaller than an average particle size (D50) of the acrylic polymer particles. 5 . The separator according to claim 4 , wherein the average particle size (D50) of the hybrid polymer particles is in the range of 100 nm to 500 nm, and the average particle size (D50) of the acrylic polymer particles is in the range of 200 nm to 700 nm. 6 . The separator according to claim 1 , wherein a mixing weight ratio of the hybrid polymer particles and the acrylic polymer particles is 8:2 to 2:8. 7 . The separator according to claim 1 , wherein a glass transition temperature Tg of the acrylic-based polymer included in the hybrid polymer particles is lower than a glass transition temperature Tg of the acrylic-based polymer included in the acrylic polymer particles by 10° C. or more. 8. The separator according to claim 7, wherein the glass transition temperature Tg of the acrylic-based polymer included in the hybrid polymer particles is 10°C to 30°C, and the glass transition temperature Tg of the acrylic-based polymer included in the acrylic polymer particles is 30°C to 50°C. 9 . The separator according to claim 1 , wherein the fluorine-based polymer is a homopolymer of vinylidene fluoride, a copolymer of vinylidene fluoride and other polymerizable monomers, or a mixture of two or more thereof. 10. The separator according to claim 9, wherein the polymerizable monomer comprises at least one selected from the group consisting of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorofluoroethylene, 1,2-difluoroethylene, perfluoro(methyl vinyl) ether, perfluoro(ethyl vinyl) ether, perfluoro(propyl vinyl) ether, perfluoro(1,3-dioxole), perfluoro(2,2-dimethyl-1,3-dioxole), trichloroethylene and fluorinated vinyl. 11. The separator according to claim 9, wherein the fluorine-based polymer is a copolymer of vinylidene fluoride and hexafluoropropylene. 12 . The separator according to claim 9 , wherein the polymerizable monomer is contained in an amount of 1 wt % to 20 wt % with respect to the copolymer. 13 . The separator according to claim 1 , wherein the acrylic-based polymer constituting the hybrid polymer particles and the acrylic-based polymer constituting the acrylic polymer particles each independently include an alkyl (meth)acrylate repeating unit having an alkyl group having 1 to 18 carbon atoms. 14 . The separator according to claim 1 , wherein the porous organic/inorganic composite coating layer includes the particulate binder polymer in an amount of 1 wt % to 30 wt % relative to the porous inorganic/organic composite coating layer. 15 . The separator according to claim 1 , wherein an average particle diameter (D50) of the inorganic particles is in the range of 200 nm to 3 μm. 16. The separator according to claim 1, wherein the porous organic/inorganic composite coating is formed by coating and drying a slurry in which the particulate binder polymer and the inorganic particles are dispersed in an aqueous dispersion medium on at least one surface of the porous polymer substrate. 17 . An electrochemical device comprising a negative electrode, a positive electrode, and a separator interposed between the positive electrode and the negative electrode, wherein the separator is the separator according to any one of claims 1 to 16. 18. The electrochemical device according to claim 17, wherein the electrochemical device is a lithium secondary battery.