Separation membrane for lithium secondary batteries and lithium secondary batteries containing the same

Abstract

According to the present invention, there is provided a separator for a lithium secondary battery having excellent heat resistance, adhesive strength and insulating properties. The separator for a lithium secondary battery according to one aspect of the present invention includes a porous polymer substrate; a first coating layer formed on one surface of the porous polymer substrate; a second coating layer formed on the other surface of the porous polymer substrate; a first aqueous binder layer formed on the surface of the first coating layer; and a second aqueous binder layer formed on the surface of the second coating layer; each of the first coating layer and the second coating layer includes inorganic particles and a coating layer binder, the inorganic particles include aluminum nitride (AlN), the first aqueous binder layer and the second aqueous binder layer include different types of particulate binders, and the particulate binders include at least one selected from a fluorine-based binder and an acrylic binder.

Description

[Technical Field]

[0001] This invention claims the benefits as of the filing date of Korean Patent Application No. 10-2022-0068533, filed with the Korean Intellectual Property Office on June 3, 2022, and all its contents are included in this invention.

[0002] This invention relates to a separator membrane for lithium secondary batteries and a lithium secondary battery containing the same. [Background technology]

[0003] As technological development and demand for mobile devices increase, the demand for rechargeable batteries as an energy source is rapidly growing. In recent years, rechargeable batteries have been used as power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs). As a result, much research is being conducted on rechargeable batteries that can meet various needs. In particular, there is a high demand for lithium-ion batteries that have high energy density, high discharge voltage, and output stability. Among these, lithium-ion batteries used as power sources for electric vehicles and hybrid electric vehicles require high output characteristics that can deliver a large output in a short time.

[0004] A lithium secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator membrane. The separator membrane requires high ionic conductivity to enhance lithium ion permeability, based on its insulating properties and high porosity to electrically isolate the positive and negative electrodes.

[0005] As a separator membrane for lithium secondary batteries, porous substrates with numerous pores and based on polymers such as polyolefins are used.

[0006] To compensate for the heat resistance and other properties of such porous polymer substrates, a separation membrane was developed in which a porous coating layer containing binder polymers and inorganic particles was formed on the surface of the polymer substrate.

[0007] The separation membrane with the aforementioned porous coating layer is manufactured by first dispersing inorganic particles in a polymer solution in which a binder polymer is dissolved in a solvent to produce a slurry, and then coating the surface of a porous polymer substrate with the produced one-component slurry and drying it. However, the separation membrane with the porous coating layer produced in this way still needs to have improved heat resistance.

[0008] On the other hand, electrode assemblies are typically manufactured through a lamination process in which the separation membrane and the electrodes are joined by heat and pressure. In recent years, a zigzag stacking (ZZS) method has been developed as a method for manufacturing electrode assemblies, in which an electrode consisting of a pair of positive and negative electrodes with a separation membrane in between is used as a unit electrode, and multiple unit electrodes are stacked in a zigzag pattern. In the ZZS method, the separation membrane and electrodes are joined by heat and pressure through a hot press process. In such processes, the higher the applied heat and pressure, the stronger the bonding force between the electrodes and the separation membrane.

[0009] However, when using an oil-based binder to manufacture the separation membrane with the aforementioned porous coating layer, a problem may arise where the wet adhesion between the electrode and the separation membrane is insufficient when the electrolyte is injected into the electrode assembly. This necessitates improving the risk of folding problems between the electrode and the separation membrane during final battery production, and the risk of Li deposition due to increased interfacial resistance between the electrode and the separation membrane.

[0010] Furthermore, achieving the high energy density of lithium-ion batteries requires thinning of the separation membrane. With porous polymer substrates of normal thickness, even if local pressure increases due to inorganic particles in the porous coating layer, the insulation is unlikely to be a problem due to sufficient thickness. However, when the thickness of the porous polymer substrate is reduced to 12 μm or less, protrusions formed by the local aggregation of inorganic particles in the porous coating layer may apply pressure to the porous polymer substrate of the separation membrane, causing damage and potentially reducing its insulation properties. [Overview of the project] [Problems that the invention aims to solve]

[0011] Therefore, according to one aspect of the present invention, the present invention aims to provide a separation membrane for lithium secondary batteries that is excellent in heat resistance, adhesive strength, and insulating properties.

[0012] Specifically, the present invention aims to provide a separation membrane for lithium secondary batteries that not only has excellent heat resistance but also excellent adhesion to electrodes, while also exhibiting excellent insulating properties due to the thinning of the separation membrane, thanks to the porous polymer substrate.

[0013] Furthermore, according to another aspect of the present invention, the present invention aims to provide a lithium secondary battery comprising a separation membrane having the aforementioned characteristics. [Means for solving the problem]

[0014] One aspect of the present invention is to provide a separation membrane for lithium secondary batteries according to the following embodiment.

[0015] According to the first concrete example, A separation membrane for lithium secondary batteries is provided, comprising: a porous polymer substrate; a first coating layer formed on one surface of the porous polymer substrate; a second coating layer formed on the other surface of the porous polymer substrate; a first aqueous binder layer formed on the surface of the first coating layer; and a second aqueous binder layer formed on the surface of the second coating layer, wherein the first coating layer and the second coating layer each independently contain inorganic particles and a coating layer binder, the inorganic particles contain aluminum nitride (AlN), the first aqueous binder layer contains a first particle-type binder, the second aqueous binder layer contains a second particle-type binder, the first particle-type binder and the second particle-type binder are different from each other, and the first particle-type binder and the second particle-type binder each independently contain a fluorine-based binder, an acrylic-based binder, or both.

[0016] According to the second example, in the first example, The first particle-type binder and the second particle-type binder each independently have an average particle size (D 50 ) can be 0.05 to 0.5 μm.

[0017] According to the third embodiment, in the first embodiment or the second embodiment, The fluorine-based binder may include poly(vinylidenefluoride) (PVDF); a copolymer of vinylidenefluoride monomer with one or more selected from trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trichloroethylene (TrCE), trichlorofluoroethylene (TCFE), chlorotrifluoroethylene (CTFE), polymethyl methacrylate (PMMA), and polyvinyl acetate (PVAc); or a mixture of two or more of these.

[0018] According to the fourth embodiment example, in any one of the first to third embodiment examples, The acrylic binder may include poly(methylmethacrylate), poly(ethylhexyl acrylate), poly(butylacrylate), poly(acrylonitrile), copolymer of ethylhexyl acrylate and methyl methacrylate, copolymer of butyl acrylate and methyl methacrylate, ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or a mixture of two or more of these.

[0019] According to the fifth example of implementation, in any one of the first to fourth examples of implementation, The coating layer binder comprises an aqueous particulate binder, and the coating layer binder may be the same as or different from the binders contained in the first aqueous binder layer and the second aqueous binder layer.

[0020] According to the sixth example of implementation, in any one of the first to fifth examples of implementation, The dry adhesion strength of the separation membrane for the lithium secondary battery to the electrode may be 70 gf / 25 mm or more.

[0021] According to the seventh example of implementation, in any one of the first to sixth examples of implementation, The wet adhesion strength of the separation membrane for the lithium secondary battery to the electrode may be 10 gf / 25 mm or more.

[0022] According to the eighth example of implementation, in any one of the first to seventh examples of implementation, The adhesive strength between the porous polymer substrate and either the first coating layer or the second coating layer, or both, may be 60 gf / 15 mm or more.

[0023] According to the 9th embodiment, in any one of the 1st to 8th embodiment examples, The thickness of the first coating layer and the second coating layer may be 5 μm or less, independently of each other.

[0024] According to the 10th embodiment, in any one of the 1st to 9th embodiment, The thickness of the first aqueous binder layer and the second aqueous binder layer may be 2 μm or less, independently of each other.

[0025] According to the 11th embodiment, in any one of the 1st to 10th embodiment, The thickness of the porous polymer substrate may be 15 μm or less.

[0026] Another aspect of the present invention provides a lithium secondary battery according to the following embodiment.

[0027] According to the 12th example, A lithium secondary battery can be provided, comprising an electrode assembly including a positive electrode, a negative electrode, and a lithium secondary battery separator interposed between the positive electrode and the negative electrode, wherein the lithium secondary battery separator is a lithium secondary battery separator of any one of the first to eleventh embodiments. [Effects of the Invention]

[0028] According to one aspect of the present invention, a separation membrane with improved heat resistance can be provided by coating a porous polymer substrate with inorganic particles.

[0029] Furthermore, it is possible to provide a separation membrane in which the adhesion between the separation membrane and the electrode is improved by applying a water-based binder layer containing a particulate binder to the coating layer of the separation membrane containing inorganic particles. In particular, it is possible to demonstrate the advantage of improved adhesion between the electrode and the separation membrane after injecting an electrolyte into the electrode assembly containing the separation membrane.

[0030] Furthermore, thinning the film allows for the provision of a separation film with uniform quality while ensuring insulation.

[0031] According to another aspect of the present invention, the improved properties of the separation membrane as described above allow the bonding process between the separation membrane and the electrode to be carried out under relaxed thermal and pressure conditions, thereby preventing and mitigating damage to the separation membrane during the bonding process with the electrode.

[0032] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the foregoing description of the invention, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to the matters described in such drawings. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram of a separation membrane according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of a separation membrane according to one embodiment of the present invention. [Modes for carrying out the invention]

[0034] The present invention will now be described in detail. Terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, based on the principle that inventors can appropriately define the concepts of terms in order to best describe their invention.

[0035] Throughout the specification of this application, when a part of it is said to "include" a certain component, unless otherwise stated, this means that it may include other components rather than excluding them.

[0036] Furthermore, the terms “comprise” and / or “comprising” as used herein identify the presence of the shapes, figures, steps, actions, members, elements, and / or groups thereof mentioned, and do not exclude the presence or addition of one or more other shapes, figures, actions, members, elements, and / or groups.

[0037] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0038] In this specification, the range of numbers expressed using the term "or" means a range of numbers that includes the values ​​listed before and after the term as the lower and upper limits, respectively. If multiple numerical values ​​are disclosed as the upper and lower limits of any given range of numbers, the range of numbers disclosed in this specification can be understood as any range of numbers whose lower limit and upper limit are any one of the multiple lower limits and any one of the multiple upper limits, respectively.

[0039] In the specification of this application, the characteristic of "having pores" means that the object contains a plurality of pores, and the structure in which these pores are connected to one another allows gaseous and / or liquid fluids to pass from one side of the object to the other.

[0040] In the specification of this application, the separation membrane has porous properties including a large number of pores and plays the role of a porous ion-conducting barrier in electrochemical elements such as lithium secondary batteries, allowing ions to pass through while blocking electrical contact between the negative electrode and the positive electrode.

[0041] The following describes in detail one aspect of the present invention: a separator membrane for lithium secondary batteries.

[0042] Figure 1 shows a schematic diagram of a separation membrane for a lithium secondary battery according to one aspect of the present invention.

[0043] A separation membrane 100 for a lithium secondary battery according to one aspect of the present invention comprises a porous polymer substrate 1; a first coating layer 11 formed on one surface of the porous polymer substrate; a second coating layer 12 formed on the other surface of the porous polymer substrate; a first aqueous binder layer 111 formed on the surface of the first coating layer; and a second aqueous binder layer 122 formed on the surface of the second coating layer, wherein the first coating layer and the second coating layer each comprise inorganic particles and a coating layer binder, the inorganic particles comprise aluminum nitride (AlN), the first aqueous binder layer comprises a first particle-type binder 110, and the second aqueous binder layer comprises a second particle-type binder 120, the first particle-type binder and the second particle-type binder are different from each other, and each independently comprises a fluorine-based binder, an acrylic-based binder, or a mixture of two or more of these.

[0044] In one embodiment of the present invention, during the manufacture of an electrode assembly comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, the separation membrane includes an aqueous binder layer on its outermost surface that contacts the positive electrode and the negative electrode, respectively. In this specification, the aqueous binder layer formed on the outermost surface of one side of the separation membrane is referred to as the first aqueous binder layer, and the aqueous binder layer formed on the outermost surface of the other side of the separation membrane is referred to as the second aqueous binder layer.

[0045] The first aqueous binder layer and the second aqueous binder layer each contain a particulate binder. In this specification, the particulate binder contained in the first aqueous binder layer is referred to as the first particulate binder, and the particulate binder contained in the second aqueous binder layer is referred to as the second particulate binder.

[0046] In this specification, the particulate binder exists in a particulate state in the aqueous binder layer. Specifically, the particulate binder has low solubility in the aqueous solvent, and as a result, it has a form that is dispersed in the aqueous solvent as particulate matter.

[0047] In one embodiment of the present invention, the aqueous solvent may be, but is not limited to, water, an aqueous solution of hydrochloric acid, an aqueous solution of sodium hydroxide, or a mixture of two or more of these.

[0048] In one embodiment of the present invention, the particle binder may have, for example, a single-phase or multi-phase particle structure such as core-shell, core-first shell-second shell, etc., but is not limited thereto.

[0049] In one embodiment of the present invention, the particle-type binder may, for example, have a spherical, elliptical, plate-like, or irregularly shaped particle form, but is not limited thereto.

[0050] In one embodiment of the present invention, the particle-type binder has an average particle size (D) of, for example, 0.05 to 0.5 μm, specifically 0.1 to 0.4 μm. 50 It may have, but is not limited to, the following characteristics.

[0051] In this specification, the average particle size (D 50 ) refers to the particle size at the point where the cumulative distribution of particle numbers according to particle size reaches 50%. The average particle size (D 50The particle size can be measured using the laser diffraction method. Specifically, the particles to be measured are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer (for example, Microtrac S3500), and the particle size distribution is calculated by measuring the difference in diffraction patterns according to the particle size as the particles pass through the laser beam. By calculating the particle size at the point where the cumulative distribution of the number of particles according to the particle size in the measuring device reaches 50%, the D 50 It can be measured.

[0052] Figure 2 shows a schematic diagram of a separation membrane for a lithium secondary battery according to one aspect of the present invention.

[0053] In one embodiment of the present invention, as shown in Figure 2, the first aqueous binder layer 111 may contain two or more first particle-type binders 110, 110' having different particle sizes. The second aqueous binder layer 122 may also contain two or more second particle-type binders 120, 120' having different particle sizes.

[0054] In the present invention, the particle-type binder comprises a fluorine-based binder, an acrylic-based binder, or a mixture of two or more of these.

[0055] The fluorine-based binder can be used without limitation as long as it can impart adhesive strength to the separation membrane for secondary batteries. The fluorine-based binder may include, for example, a homopolymer of vinylidene fluoride monomer, i.e., polyvinylidene fluoride (poly(vinylidenefluoride), PVDF); a copolymer of vinylidene fluoride monomer with one or more selected from trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trichloroethylene (TrCE), trichlorofluoroethylene (TCFE), chlorotrifluoroethylene (CTFE), polymethyl methacrylate (PMMA), and polyvinyl acetate (PVAc); or a mixture of two or more of these.

[0056] In one embodiment of the present invention, the fluorine-based binder may contain polyvinylidene fluoride.

[0057] The acrylic binder can be used without limitation as long as it can impart adhesive strength to the separation membrane for secondary batteries. The acrylic binder may be, for example, a homopolymer of acrylic monomers, a copolymer of two or more acrylic monomers, or a mixture of two or more of these. Specifically, the acrylic binder may include, for example, polymethyl methacrylate (poly(methylmethacrylate)), polyethylhexyl acrylate (poly(ethylhexyl acrylate)), polybutyl acrylate (poly(butylacrylate)), polyacrylonitrile (poly(acrylonitrile)), copolymers of ethylhexyl acrylate and methyl methacrylate, copolymers of butyl acrylate and methyl methacrylate, ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or mixtures of two or more of these.

[0058] In one embodiment of the present invention, the acrylic binder may contain polymethyl methacrylate.

[0059] In the present invention, the first aqueous binder layer includes a first particle-type binder, and the second aqueous binder layer includes a second particle-type binder, wherein the first particle-type binder and the second particle-type binder are different from each other. According to one embodiment of the present invention, by using the first particle-type binder and the second particle-type binder which is different from the first particle-type binder, the adhesion strength of the separation film to the electrode can be further increased in both dry and wet conditions.

[0060] In one embodiment of the present invention, the first particle-type binder represents an aggregate of particle-type binders contained in the first aqueous binder layer. That is, the first particle-type binder may contain one or more particle-type binders, and may also contain particle-type binders having different forms from each other. For example, the first particle-type binder may represent an aggregate containing two or more of the fluorine-based binders listed above. Alternatively, the first particle-type binder may represent an aggregate containing two or more of the acrylic-based binders listed above. Furthermore, the first particle-type binder may contain one or more of the fluorine-based binders listed above, and one or more of the acrylic-based binders listed above.

[0061] In another embodiment of the present invention, the second particle-type binder also represents an aggregate of particle-type binders contained in the second aqueous binder layer.

[0062] In one embodiment of the present invention, the aqueous binder layer formed on the outermost surface of the separation membrane in contact with the positive electrode of the electrode assembly contains a fluorine-based binder, which provides an advantageous effect in terms of adhesion between the separation membrane and the electrode (i.e., the positive electrode). Furthermore, the aqueous binder layer formed on the outermost surface of the separation membrane in contact with the negative electrode of the electrode assembly contains an acrylic-based binder, which also provides an advantageous effect in terms of adhesion between the separation membrane and the electrode (i.e., the negative electrode).

[0063] Specifically, in one embodiment of the present invention, if the first particle-type binder contains one or more of the fluorine-based binders described above, the second particle-type binder may contain one or more of the acrylic-based binders described above. In this case, if the first particle-type binder contains the fluorine-based binder and the second particle-type binder contains the acrylic-based binder, the first aqueous binder layer may be the outermost surface of the separation membrane that comes into contact with the positive electrode during the manufacture of the electrode assembly using the separation membrane, and the second aqueous binder layer may be the outermost surface of the separation membrane that comes into contact with the negative electrode.

[0064] In one embodiment of the present invention, the first particle-type binder may further contain an acrylic binder in a quantity that does not hinder the objective of the present invention, in addition to the fluorine-based binder, and the present invention is not limited thereto.

[0065] In other embodiments of the present invention, the second particle-type binder may further contain a fluorine-based binder in a quantity that does not impede the purpose of the present invention, in addition to the acrylic-based binder, and the present invention is not limited thereto.

[0066] In one embodiment of the present invention, the first aqueous binder layer and the second aqueous binder layer may each independently contain 100% by weight of binder. Furthermore, the first aqueous binder layer and the second aqueous binder layer may each independently further contain a dissolved binder in a content that does not hinder the objective of the present invention, in addition to the particulate binder, and the present invention is not limited thereto.

[0067] In one embodiment of the present invention, the thickness of the first aqueous binder layer and the second aqueous binder layer can be independently, for example, 2 μm or less, specifically 0.1 μm to 1.5 μm, more specifically 0.3 μm to 1 μm, 0.4 μm to 0.8 μm, or 0.5 μm. While having the thickness of each of the aqueous binder layers within the aforementioned ranges can provide advantageous effects in terms of the adhesion and air permeability of the separation membrane, the present invention is not limited thereto.

[0068] In this specification, unless otherwise defined, the thickness of each layer can be measured by scanning electron microscope (SEM) observation of the separation film cross-section, or by using a known thickness measuring instrument. The known thickness measuring instrument may be, but is not limited to, the Mitutoyo VL-50S-B instrument, which is a contact-type thickness measuring instrument.

[0069] In one embodiment of the present invention, the first aqueous binder layer and the second aqueous binder layer may each be formed independently by applying a slurry in which the particulate binder is dispersed in a suitable aqueous solvent to the surface of the coating layer and drying it, but the manufacturing method is not limited thereto.

[0070] As mentioned above, the aqueous solvent may include, but is not limited to, water, aqueous hydrochloric acid solution, aqueous sodium hydroxide solution, or a mixture of two or more of these.

[0071] In one embodiment of the present invention, the slurry in which the particulate binder is dispersed may have a solid content of, for example, 2 to 20% by weight, specifically 3 to 10% by weight, but the present invention is not limited thereto.

[0072] In the present invention, the first aqueous binder layer and the second aqueous binder layer are formed on the surfaces of the first coating layer and the second coating layer, respectively.

[0073] In one embodiment of the present invention, the first aqueous binder layer and the second aqueous binder layer may be formed in contact with the surfaces of the first coating layer and the second coating layer, respectively.

[0074] In the present invention, the first coating layer and the second coating layer each contain inorganic particles and a coating layer binder.

[0075] In the present invention, the inorganic particles include aluminum nitride (AlN) from the viewpoint of ensuring the heat resistance and insulation properties of the separation membrane and improving adhesion to the porous substrate within the separation membrane, but the effects of the present invention are not limited to this. According to one embodiment of the present invention, by using aluminum nitride as the inorganic particles, the dielectric breakdown voltage of the separation membrane can be further increased compared to other inorganic particles.

[0076] In one embodiment of the present invention, the first coating layer and the second coating layer may each independently further contain electrochemically stable inorganic particles other than aluminum nitride (AlN) that can be used in a separation membrane for a secondary battery. For example, in one embodiment of the present invention, the inorganic particles that may further be included in the first coating layer and the second coating layer may be within the operating voltage range of the battery to which it is applied (e.g., Li / Li + It is not particularly limited as long as oxidation and / or reduction reactions do not occur at a voltage of 0-5V (based on the reference voltage).

[0077] In one embodiment of the present invention, if at least one of the first coating layer and the second coating layer further contains additional inorganic particles other than aluminum nitride as inorganic particles, the aluminum nitride content may be, for example, 5 to 90% by weight, specifically 10 to 85% by weight, based on the total weight of the inorganic particles contained in one layer. While the aluminum nitride content being within the aforementioned range can provide advantageous effects in terms of the heat resistance of the separation membrane, the present invention is not limited thereto.

[0078] Examples of inorganic particles that may be included as mentioned above include high dielectric constant inorganic particles with a dielectric constant of 1 or more, preferably 10 or more, inorganic particles having piezoelectric properties, and inorganic particles having lithium ion transport capability.

[0079] Examples of the high dielectric constant inorganic particles include SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, AlOOH, Al(OH)3, TiO2, and SiC, and can be used in mixtures of one or more of these, but is not limited thereto.

[0080] The inorganic particles having piezoelectricity mean a substance that is a non-conductor under normal pressure but has the property of conducting electricity due to changes in its internal structure when a certain pressure is applied. Such piezoelectric inorganic particles have a high relative permittivity value of 100 or more. Also, when a certain pressure is applied and it is stretched or compressed, charges are generated. One surface becomes positively charged and the opposite surface becomes negatively charged, respectively, thereby generating a potential difference between the two surfaces. When using such piezoelectric inorganic particles, when an internal short circuit occurs between the two electrodes due to an external impact such as local crush or nail, a potential difference is generated within the particles due to the piezoelectricity of the inorganic particles, and thereby electron transfer between the two electrodes, that is, a flow of a minute current occurs, whereby a gentle decrease in the battery voltage and an improvement in safety due to this can be achieved. Examples of inorganic particles having piezoelectricity include BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1-x La x Zr 1-y Ti y O3 (PLZT), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3 (PMN-PT), hafnium oxide (HfO2) or mixtures thereof, etc., but are not limited thereto.

[0081] The inorganic particles having lithium ion transfer ability refer to inorganic particles that contain lithium element but have the function of moving lithium ions without storing lithium. Inorganic particles having lithium ion transfer ability can transfer and move lithium ions due to a kind of defect existing inside the particle structure, so the lithium ion conductivity in the battery is improved, and thereby the battery performance can be improved. Examples of inorganic particles having lithium ion transfer ability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z(PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), such as 14Li2O - 9Al2O3 - 38TiO2 - 39P2O5, and (LiAlTiP) x O y series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), Li 3.25 Ge 0.25 P 0.75 S4, and other lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride such as Li3N (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 - based glass such as Li3PO4 - Li2S - SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), P2S5 - based glass such as LiI - Li2S - P2S5 (Li<000003 A>P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or mixtures thereof, etc., but not limited thereto.

[0082] In one embodiment of the present invention, the inorganic particles may have an average particle size (D 50 ) of, for example, 10 to 1,500 nm, specifically 150 to 1,000 nm. When the average particle size (D 50 ) of the inorganic particles is within the above - mentioned range, it can show an advantageous effect from the viewpoints of the adhesion and porosity of the coating layer, but the present invention is not limited thereto.

[0083] In the present invention, the first coating layer and the second coating layer contain a coating layer binder together with inorganic particles containing aluminum nitride.

[0084] It should be noted that there seems to be an error in the original text where "0 < x < 3, 0 < y < 2, 0 < z < A" in is likely a mistake. I've translated it as "0 < x < 3, 0 < y < 2, 0 < z < 4" based on the context. If this is incorrect, please correct the original text for a more accurate translation.The coating layer binder may provide adhesion to the porous polymer substrate and electrodes of the coating layer while connecting and fixing the inorganic particles together.

[0085] In one embodiment of the present invention, the coating layer binder is, for example, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-co-trichloroethylene copolymer, polymethyl methacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide. It may be any one polymer selected from the group consisting of oxide, polyarylate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methylcellulose, or a mixture of two or more of these. However, it is not limited to this.

[0086] In one embodiment of the present invention, the type of coating layer binder contained in the coating layer may be the same as or different from the type of particulate binder contained in the aqueous binder layer formed on the surface of the coating layer. Specifically, the type of coating layer binder contained in the coating layer can be selected independently of the type of particulate binder contained in the aqueous binder layer adjacent to the coating layer.

[0087] In one embodiment of the present invention, the coating layer binder may include, for example, an aqueous particulate binder. When the coating layer binder includes an aqueous particulate binder, it can be shown that the aqueous particulate binder has low solubility in an aqueous solvent and thus has a form in which it is dispersed in particulate form in the aqueous solvent. Here, the aqueous solvent may include, but is not limited to, water, an aqueous hydrochloric acid solution, an aqueous sodium hydroxide solution, or a mixture of two or more of these.

[0088] In one embodiment of the present invention, the glass transition temperature (Tg) of the coating layer binder may be, for example, -50°C to 0°C, specifically -30°C to -20°C, or -25°C. While having the glass transition temperature of the coating layer binder within the aforementioned range may have advantageous effects in terms of the adhesion strength of the separation film, the present invention is not limited thereto.

[0089] In this specification, the glass transition temperature (Tg) may represent a value measured, for example, by dynamic mechanical analysis (DMA). For example, the glass transition temperature may represent a value measured by the DMA method specified in ASTM D4065.

[0090] In one embodiment of the present invention, the compositions of the first coating layer and the second coating layer may be configured independently of each other. For example, the compositions of the first coating layer and the second coating layer may be the same, or they may be different.

[0091] In one embodiment of the present invention, having the same composition for the first coating layer and the second coating layer can provide advantageous effects in terms of the thermal conductivity and insulating properties of the separation film, but the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the first coating layer and the second coating layer may each independently contain the inorganic particles and the coating layer binder in a weight ratio of 1:99 to 50:50. The weight ratio can be appropriately adjusted within the above range, for example, based on a total of 100% by weight of the inorganic particles and the coating layer binder, the coating layer binder may be 1% by weight or more, 5% by weight or more, or 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more, and the inorganic particles may be 70% by weight or more, 75% by weight or more, 80% by weight or more, 85% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more. In one embodiment of the present invention, the coating layer is preferably porous in terms of ion permeability. In one embodiment of the present invention, if the content of the coating layer binder is less than 1% by weight, not only the adhesive strength between the porous polymer substrate and the coating layer, but also the adhesive strength between the coating layer and the aqueous binder layer may be insufficient. If the content is excessively high, the porosity of the coating layer may decrease, which may increase the resistance inside the battery and degrade the electrochemical properties of the battery.

[0093] For example, in one embodiment of the present invention, the first coating layer and the second coating layer may each independently have a porosity of 5 to 95 volume%, 10 to 95 volume%, 20 to 90 volume%, 30 to 80 volume%, or 40 to 70 volume%. The porosity can be adjusted to the aforementioned ranges in terms of ensuring sufficient pathways for ions to pass through, ensuring ionic conductivity, and ensuring heat resistance and adhesion. Therefore, considering such electrochemical properties, the porosity of the porous coating layer can be appropriately adjusted within the above range.

[0094] In this specification, the term "porosity" refers to the ratio of the volume occupied by pores to the total volume in a given structure, using % as its unit, and can be used in the same sense as terms such as void ratio and porosity. In the present invention, the measurement of porosity is not particularly limited, and according to one embodiment of the present invention, it can be measured, for example, by the BET (Brunauer-Emmett-Teller) measurement method using nitrogen gas, or by the mercury osmosis method (Hg porosimeter) and ASTM D2873. Alternatively, the true density of the separation membrane can be calculated from the density of the separation membrane (apparent density) and the composition ratio of the materials contained in the separation membrane and the density of each component, and the porosity of the separation membrane can be calculated from the difference between the apparent density and the true density.

[0095] In one embodiment of the present invention, the total thickness of the coating layer can be appropriately adjusted, for example, within the range of 1 μm to 10 μm. The total thickness of the coating layer is the sum of the thicknesses of the coating layers on all sides formed on the surface of the porous polymer substrate, i.e., the first coating layer and the second coating layer. When the total thickness of the coating layer satisfies the aforementioned range, it is advantageous for improving the heat resistance effect of inorganic particles and for reducing the overall thickness of the battery, and therefore may be advantageous for improving the energy density of the battery, but the present invention is not limited thereto.

[0096] In one embodiment of the present invention, the thickness of the first coating layer and the second coating layer can be independently, for example, 5 μm or less, 4 μm or less, and specifically 1 to 3 μm.

[0097] In one embodiment of the present invention, the first coating layer and the second coating layer may each be formed by applying and drying a slurry in which the coating layer binder is dissolved on one surface of the porous polymer substrate and the aluminum nitride-containing inorganic particles are dispersed.

[0098] In one embodiment of the present invention, the slurry for forming the coating layer may be manufactured by adding the coating layer binder and inorganic particles containing aluminum nitride to a suitable solvent and mixing them. Specifically, it may be manufactured by first adding the coating layer binder to a solvent to produce a binder solution, and then adding and mixing the inorganic particles thereto, or by adding the inorganic particles to a solvent and then adding and mixing the coating layer binder, but is not limited to these methods.

[0099] In one embodiment of the present invention, the slurry for forming the coating layer may be, for example, an aqueous slurry, in which case the aqueous solvent may be, but is not limited to, water, an aqueous hydrochloric acid solution, an aqueous sodium hydroxide solution, or a mixture of two or more of these.

[0100] In one embodiment of the present invention, the porous polymer substrate refers to a film made of a polymer material having a large number of pores, which is commonly used in separation membranes for lithium secondary batteries.

[0101] In one embodiment of the present invention, the porous polymer substrate may be a polymer film made of a porous polyolefin material. When a polyolefin material is used as the porous polymer substrate, the difference between the shutdown temperature and the meltdown temperature of the separation membrane for lithium secondary batteries can be greatly realized, which is advantageous in improving the stability of the separation membrane, but the effects of the present invention are not limited to this.

[0102] In one embodiment of the present invention, the porous polyolefin material may be, but is not limited to, polyethylene; polypropylene; polybutylene; polypentene; polyhexene; polyoctene; copolymers of two or more of ethylene, propylene, butene, pentene, 4-methylpentene, hexene, hepsene, and octene; or mixtures thereof. In particular, the polyethylene may be low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and among these, high-density polyethylene, which has a high degree of crystallinity and a high melting point of the resin, may be the most preferred.

[0103] In one embodiment of the present invention, when the porous polymer substrate contains both polyethylene and polypropylene as polyolefins, it is possible to simultaneously improve physical properties such as shutdown characteristics and mechanical strength, but the invention is not limited to this.

[0104] In one embodiment of the present invention, the porosity of the porous polymer substrate may be in the range of, for example, 30 to 70 by volume. For example, the porosity of the porous polymer substrate may be 42 by volume or more, 45 by volume or more, 50 by volume or more, or 55 by volume or more within the aforementioned range. Alternatively, the porosity of the porous polymer substrate may be 60 by volume or less, 55 by volume or less, or 55 by volume or less within the aforementioned range. For example, the porosity of the porous polymer substrate may have a value of 40 by volume or more and 65 by volume or less.

[0105] In one embodiment of the present invention, the pores of the porous polymer substrate have a diameter (D) relative to the longest diameter of the pores. 50 The diameter (D) may be in the range of 10 nm to 70 nm, and within that range, it may be 65 nm or less, or 60 nm or less. Considering the improvement of the resistive characteristics of the separation membrane, it is preferable that the pore size and distribution within the separation membrane are uniform. Therefore, in the present invention, while the pore diameter satisfies the above range, the pore size is uniform and the distribution is uniform, thereby exhibiting excellent resistive characteristics. 50 ) is the aforementioned D 50 The above-mentioned provisions regarding particle size can be applied mutatis mutandis. In short, the above-mentioned "diameter (D 50 )" refers to the diameter at the point where the cumulative distribution of stomata based on diameter reaches 50%.

[0106] In one embodiment of the present invention, the size of the pores can be measured using a capillary flow porometer. This method involves wetting the pores of the separation membrane with a liquid whose surface tension is known, and then applying air pressure to measure the pressure at which the first flow rate is generated (bubble point = max pore). A specific example of such a capillary flow porometer is the CFP-1500-AE from Porous Materials.

[0107] In one embodiment of the present invention, the thickness of the porous polymer substrate may be, for example, 15 μm or less, specifically 5 μm to 12 μm. While having a porous polymer substrate thickness within the aforementioned range can provide advantageous effects in terms of thinning the lithium secondary battery and increasing its energy density, the invention is not limited to this. Specifically, when the thickness of the porous polymer substrate is reduced, there is a problem in that protrusions formed by the local aggregation of inorganic particles in the porous coating layer apply pressure to the porous polymer substrate of the separation membrane, causing damage and reducing its insulating properties. According to one embodiment of the present invention, even if the thickness of the porous polymer substrate is reduced to within the aforementioned numerical range, the dielectric breakdown voltage of the separation membrane can be increased and the insulating properties can be further improved by using aluminum nitride as the inorganic particles in the coating layer.

[0108] In one embodiment of the present invention, the porous polymer substrate may be manufactured by a dry method in which a polymer is melted and pressed into a sheet, and then stretched to induce microcracks between the lamellae, which are the crystalline parts of the polymer, thereby forming micropores. Alternatively, the porous polymer substrate may be manufactured by a wet method in which a polymer is kneaded with diluents at a high temperature to create a single phase, the polymer material and diluents are separated during the cooling process, and then the diluents are extracted to form pores.

[0109] A separation membrane according to one aspect of the present invention can exhibit excellent adhesion to electrodes.

[0110] The separation membrane can exhibit excellent performance in at least one of the properties of dry adhesion and wet adhesion to the electrode.

[0111] In this specification, the dry adhesive strength refers to the adhesive strength of the electrode assembly, in which the separation membrane and the electrode are joined, before the electrolyte is impregnated.

[0112] In this specification, the wet adhesive strength refers to the adhesive strength after the electrode assembly, in which the separation membrane and the electrode are joined, has been impregnated with an electrolyte.

[0113] In one embodiment of the present invention, the separation membrane described above can exhibit a dry adhesion strength to the electrode of, for example, 70 gf / 25 mm or more. Specifically, the dry adhesion strength to the electrode may be 80 gf / 25 mm or more, or 100 gf / 25 mm or more, and more specifically, it may have a value of 150 gf / 25 mm to 250 gf / 25 mm, or 160 gf / 25 mm to 200 gf / 25 mm.

[0114] In one embodiment of the present invention, the dry adhesive force with the electrode may be the dry adhesive force with the negative electrode.

[0115] In this specification, the dry adhesion strength to the negative electrode is expressed as the value measured by the following method: Natural graphite, SBR, CMC, and carbon black (weight ratio 90:2.5:2.5:5) are added to water to obtain a negative electrode slurry, and the negative electrode slurry is applied to a copper thin film (thickness 20 μm) at a density of 5 mg / cm². 2 After applying the coating with the specified loading amount, it is dried. Next, it is rolled at 90°C and 8.5 MPa and cut into 60 mm (length) x 25 mm (width) pieces to prepare a standard negative electrode. Next, the separation membrane to be evaluated is cut to a size of 70 mm (length) x 25 mm (width), and then positioned so that it is in contact with the prepared standard negative electrode and the coating layer. A test specimen is then prepared by laminating it using a press at 60°C, 6.5 MPa, and 1 s. The prepared test specimen is attached to a glass plate using double-sided tape and fixed so that the negative electrode faces the glass plate. The separation membrane portion of the test specimen is peeled off at an angle of 180° at a speed of 300 mm / min at 25°C using an Instron UTM device, and the strength at this time is measured to determine the dry adhesive strength.

[0116] In one embodiment of the present invention, the separation membrane described above can exhibit a wet adhesion strength to the electrode of, for example, 10 gf / 25 mm or more. Specifically, the wet adhesion strength to the electrode may have values ​​of 15 gf / 25 mm or more, 20 gf / 25 mm or more, or 30 gf / 25 mm or more, more specifically 30 gf / 25 mm to 80 gf / 25 mm, 35 gf / 25 mm to 70 gf / 25 mm, or 36.5 gf / 25 mm to 60 gf / 25 mm.

[0117] In this specification, the wet adhesion strength of the separation membrane to the positive electrode is expressed as the value measured by the following method. First, after assembling the monocell, the electrolyte is injected to activate the electrode assembly and impregnate it with the electrolyte. Then, the electrode assembly removed from the monocell is sampled in a width of 25 mm, and the electrode assembly is fixed to the glass plate using double-sided tape so that the electrodes of the sampled electrode assembly face the glass plate. The separation membrane portion of the test piece is peeled off at a 90° angle at a speed of 200 mm / min at 25°C using an Instron UTM device, and the strength at this time is measured and defined as the wet adhesion strength.

[0118] In one embodiment of the present invention, when assembling the monocell, the positive electrode is a positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 A slurry for the positive electrode active material layer with a solid content of 50 wt% can be prepared by mixing O2), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) with water in a weight ratio of 97.5:0.7:0.14:1.66, and then applying and drying this slurry to the surface of a current collector (10 μm thick) to prepare a positive electrode (active material layer thickness of 120 μm), but is not limited to this.

[0119] In one embodiment of the present invention, when assembling the monocell, the negative electrode can be prepared by mixing graphite, a conductive material (carbon black), a dispersant, and a fluorine-based binder resin with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the negative electrode active material layer with a solid content of 50 wt%, and then applying and drying this slurry onto the surface of a current collector (thickness 10 μm) to prepare a negative electrode (active material layer thickness 120 μm), but is not limited thereto.

[0120] In one embodiment of the present invention, the activation step for preparing the electrode assembly may be carried out at 55°C with a charge state of charge of 60%, but is not limited thereto.

[0121] According to one embodiment of the present invention, the separation membrane may not only have excellent adhesion to the electrode, but also excellent adhesion (peel strength) between the porous polymer substrate and the coating layer.

[0122] In one embodiment of the present invention, the separation membrane may exhibit an adhesive strength of, for example, 60 gf / 15 mm or more between the porous polymer substrate and the first coating layer and the second coating layer, respectively.

[0123] In this specification, the adhesive strength between the porous polymer substrate and the coating layer, i.e., the peel strength, can be expressed as a value measured by, for example, cutting the separation film into pieces measuring 80 mm (length) x 15 mm (width) to prepare two test pieces from each piece, attaching the two test pieces together with double-sided tape, peeling them off at a speed of 300 mm / min at 25°C at a 180° angle, and measuring the strength at that time.

[0124] According to one embodiment of the present invention, the separation membrane can exhibit excellent effects in terms of low thermal shrinkage characteristics and high dielectric breakdown voltage characteristics.

[0125] In one embodiment of the present invention, the separation membrane may have low thermal shrinkage coefficients in both the mechanical direction (MD) and the transverse direction (TD).

[0126] In this specification, the mechanical direction (MD) of the separation membrane indicates the mechanical direction of the porous polymer substrate of the separation membrane, and the transverse direction (TD) of the separation membrane indicates the direction perpendicular to the mechanical direction.

[0127] The mechanical orientation of the porous polymer substrate indicates the production direction of the porous polymer substrate during the manufacturing process. Specifically, the mechanical orientation of the porous polymer substrate coincides with the orientation direction of the fibers within the porous polymer substrate, and can be confirmed through the orientation direction of the fibers within the manufactured porous polymer substrate. For example, the orientation direction of the fibers within the porous polymer substrate can be confirmed through a scanning electron microscope (SEM) image of the cross-section of the porous polymer substrate. It can also be confirmed through an SEM image of the cross-section of the separation membrane containing the porous polymer substrate. The orientation direction of the fibers confirmed through the SEM image can be confirmed to be the mechanical orientation (MD) of the porous polymer substrate and the mechanical orientation (MD) of the separation membrane.

[0128] In one embodiment of the present invention, the thermal shrinkage rate of the separation membrane may be, for example, 10% or less, 5% or less, 3% or less, 2% or less, 1% or less, or 0% in both the mechanical direction (MD) and the transverse direction (TD).

[0129] In this specification, the thermal shrinkage rate of the separation membrane can be evaluated by the following method. The separation membrane to be evaluated is cut to a size of 50 mm x 50 mm and placed between A4 sheets of paper. After placing it in a 120°C convection oven for 1 hour, the thermal shrinkage rates in the mechanical direction (MD) and transverse direction (TD) are measured. At this time, the thermal shrinkage rate (%) is calculated as [(initial length - length after heat treatment at 120°C / 1 hour) / (initial length)] × 100.

[0130] In one embodiment of the present invention, the thermal shrinkage rate of the separation membrane can be calculated based on a value measured after storing the separation membrane at 150°C for 30 minutes immediately after manufacturing, for the sake of accuracy of the measurement.

[0131] In one embodiment of the present invention, the dielectric breakdown voltage of the separator film may be, for example, 1,000V or more, specifically 1,500V or more, and more specifically 1,500V to 2,500V.

[0132] In this specification, the dielectric breakdown voltage of the separation membrane is expressed as the value measured by the following method. The dielectric breakdown voltage is measured using an AC / DC / IR Hi-Pot tester. Specifically, a 10×10cm piece of release PET is laminated to the top / bottom of a 5×5cm piece of separation membrane to be evaluated. At this time, the release surface of the release PET is in contact with the separation membrane. A compressed separation membrane sample is prepared by hot pressing the separation membrane laminated with PET at a temperature of 70°C and a pressure of 5.2MPa for 10 seconds. The prepared compressed separation membrane sample is placed between aluminum fixtures (upper fixture diameter 30mm, lower fixture 50×100mm), and the voltage at which the fail condition (>0.5mA, 3sec) occurs is measured using a Hi-pot tester. At this time, the measurement conditions are set to DC, current 0.5mA, and boost voltage 100V / s (up to 3kV). The measured value is expressed as the average of 30 samples.

[0133] In one embodiment of the present invention, the separation membrane may have excellent air permeability by sequentially comprising a coating layer and an aqueous binder layer on both sides of a porous polymer substrate.

[0134] In one embodiment of the present invention, the separation membrane may have an air permeability that is, for example, 10% or more, specifically 15% or more, compared to the air permeability of the porous polymer substrate.

[0135] In this specification, the air permeability (air permeability time, Gurley) of the separation membrane and the porous polymer substrate can be measured by the ASTM D-2873 method. The Gurley value is measured according to the Japanese Industrial Standard (JIS) Gurley measurement method using a Gurley type densometer (No. 158) manufactured by Toyoseiki Co., Ltd. The air permeability value is measured when 100 ml of air is passed through the separation membrane at a pressure of 12.2 in H2O, and the air permeability time is 1 in 2 This is expressed as the time (in seconds) it takes for air to pass through the cross-section, i.e., the permeability time.

[0136] Using the measured values ​​of air permeability obtained above, the rate of increase in air permeability can be evaluated according to the following formula.

[0137] Permeability increase rate (%) = [(Permeability of manufactured separation membrane - Permeability of porous polymer substrate) / Permeability of porous polymer substrate] × 100

[0138] As described above, the separation membrane according to one aspect of the present invention may have one or more properties among excellent adhesion to electrodes, low thermal shrinkage rate, high dielectric breakdown voltage, and high air permeability, but the effects of the present invention are not limited to these.

[0139] In another aspect of the present invention, a lithium-ion secondary battery comprising the separation membrane is provided. The battery comprises an electrode assembly comprising a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode, the separation membrane being an embodiment of the present invention.

[0140] In one embodiment of the present invention, the positive electrode and the negative electrode are not particularly limited, and can be used in which the electrode active material is bonded to a current collector according to a conventional method known in the art.

[0141] Among the electrode active materials, non-restrictive examples of positive electrode active materials include conventional positive electrode active materials that can be used in the positive electrodes of conventional electrochemical elements, such as lithium transition metal oxides; lithium metallic iron phosphorus oxides; lithium-nickel-manganese-cobalt oxides; oxides in which some of the lithium-nickel-manganese-cobalt oxides are substituted with different transition metals; or two or more of these may be included, but are not limited thereto. Specifically, the positive electrode active material may be, for example, a layered compound such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x is 0 to 0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (where M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M x Lithium manganese composite oxide represented by O2 (where M = Co, Ni, Fe, Cr, Zn, or Ta, and x = 0.01 to 0.1) or Li2Mn3MO8 (where M = Fe, Co, Ni, Cu, or Zn); lithium metal phosphorus oxide LiMPO4 (where M = Fe, CO, Ni, or Mn); lithium nickel-manganese-cobalt oxide Li 1+x (Ni a Co b Mn c ) 1-x O2 (x=0~0.03, a=0.3~0.95, b=0.01~0.35, c=0.01~0.5, a+b+c=1); Lithium nickel-manganese-cobalt oxide, in which part of the oxide is substituted with aluminum. a [Ni b Co c Mn d Ale 1-f M1 f O2 (M1 is one or more selected from the group consisting of Zr, B, W, Mg, Ce, Hf, Ta, La, Ti, Sr, Ba, F, P, and S; 0.8 ≦ a ≦ 1.2, 0.5 ≦ b ≦ 0.99, 0 < c < 0.5, 0 < d < 0.5, 0.01 ≦ e ≦ 0.1, 0 ≦ f ≦ 0.1); In lithium-nickel-manganese-cobalt oxide, an oxide in which part is substituted with other transition metals, Li 1+x (Ni a Co b Mn c M d ) 1-x O2 (x = 0 to 0.03, a = 0.3 to 0.95, b = 0.01 to 0.35, c = 0.01 to 0.5, d = 0.001 to 0.03, a + b + c + d = 1, M is any one selected from the group consisting of Fe, V, Cr, Ti, W, Ta, Mg, and Mo.). Disulfide compounds; Examples include, but are not limited to, Fe2(MoO4)3.

[0142] Among the electrode active materials, non-limiting examples of the negative electrode active material include ordinary negative electrode active materials that can be used for the negative electrode of conventional electrochemical elements. In particular, carbon such as lithium metal oxide, graphitized carbon, and graphite-based carbon; sulfur (S); Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8) and other metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials; lithium titanium composite oxides, and one or more mixtures selected from titanium oxides may be included. ​

[0143] Non-limiting examples of the positive electrode current collector include foil made from aluminum, nickel, or a combination thereof, and non-limiting examples of the negative electrode current collector include foil made from copper, gold, nickel, or a copper alloy, or a combination thereof.

[0144] In one embodiment of the present invention, the electrode assembly is provided with the aforementioned lithium secondary battery separation membrane in a strip shape, and one or more pairs of positive and negative electrodes are provided on the upper and lower surfaces, respectively, with a predetermined distance between them, sandwiching the strip-shaped separation membrane. The assembly is then folded in a zigzag shape, and then hot-pressed to apply heat and / or pressure, and manufactured by a zig-zag stacking (ZZS) process.

[0145] In one embodiment of the present invention, since the separation membrane has excellent heat resistance and electrode adhesion, it is possible to demonstrate the advantage that the hot pressing process for fixing the separation membrane and the electrode can be carried out under milder conditions than the conventional pressurizing and / or heating process for laminating the separation membrane and the electrode.

[0146] For example, even if the hot pressing process is carried out at a temperature of 50°C to 110°C and a pressure of 3 MPa to 10 MPa, the separation membrane can exhibit excellent adhesion to the electrodes (positive electrode, negative electrode) while also demonstrating the advantages of excellent ionic conductivity, heat resistance, and insulation properties of the separation membrane.

[0147] In one embodiment of the present invention, the lithium secondary battery is characterized in that the electrode assembly described above is housed in a case. The case can be one of those commonly used as battery cases and is not particularly limited in shape to suit the battery's application. For example, the case may be cylindrical, rectangular, pouch-type, or coin-type, using a can. Once such an electrode assembly is completed, it can be housed in the case in a conventional manner, an electrolyte solution can be injected, and the case can be sealed to manufacture a lithium secondary battery.

[0148] Non-limiting examples of the electrolyte include salts having a structure such as A + B - where A + is an alkali metal cation such as Li + Na + K + or a combination thereof, and B - is an anion such as PF6 - BF4 - Cl - Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - or a combination thereof, and salts dissolved or dissociated in an organic solvent composed of 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), gamma-butyrolactone (γ-butyrolactone) or a mixture thereof, but not limited thereto.

[0149] Furthermore, according to another aspect of the present invention, a battery module including the lithium secondary battery as a unit battery, a battery pack including the battery module, and a device including the battery pack as a power source can be provided. Specific examples of the device include, but are not limited to, a power tool powered by a battery-powered motor; electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0150] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various different forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average knowledge in the industry.

[0151] [Manufacturing example: Manufacturing of separation membranes] Example 1 A separation membrane with the following structure was manufactured: second aqueous binder layer / second coating layer / porous polymer substrate / first coating layer / first aqueous binder layer.

[0152] [Preparation of porous polymer substrate] As a porous polymer substrate, we prepared a wet polyethylene substrate (9 μm thick) with a porosity of 45% from Toray Industries, Inc.

[0153] [Formation of the first and second coating layers] A slurry was prepared in which inorganic particles and a coating layer binder were dispersed as follows.

[0154] After adding 4 parts by weight of cyanoethyl polyvinyl alcohol (MW = 100,000 g / mol) to 100 parts by weight of water, it was slowly dispersed. Then, aluminum nitride particles (AlN) with an average particle size (D 50 ) of 500 nm were added to the suspension in which cyanoethyl polyvinyl alcohol was dispersed and mixed, and sufficiently stirred and dispersed to produce a slurry for forming a coating layer. The solid content of the produced slurry was 23 wt%, and the weight ratio of aluminum nitride particles and cyanoethyl polyvinyl alcohol in the slurry was 95:5.

[0155] The produced slurry was applied to both sides of the prepared porous polymer substrate, and then sufficiently dried with warm air at 60 °C to form first and second coating layers each having a thickness of 2 μm.

[0156] 〔Formation of the first and second aqueous binder layers〕 A slurry in which a particulate binder was dispersed was prepared as follows.

[0157] PVDF-HFP (MW = 400,000 g / mol, average particle size (D 50 ) 250 nm, HFP 5 wt%) was dispersed in water as an aqueous particulate binder to produce a slurry for forming the first aqueous binder layer. The solid content of the produced slurry was 5 wt%. <​​​​​​​The prepared first aqueous binder layer forming slurry and the second aqueous binder layer forming slurry were coated onto the surfaces of the first coating layer and the second coating layer, respectively, and dried at 60°C to form aqueous binder layers with a thickness of 0.5 μm.

[0160] Example 2 The separation membrane is manufactured in the same manner as in Example 1, except that the slurry for forming the first aqueous binder layer in Example 1 is replaced with polyvinylidene fluoride (poly(vinylidenefluoride), PVDF) (Mw = 400,000 g / mol, average particle size (D)) instead of PVDF-HFP. 50 Using ()=250nm) in the slurry for forming the second aqueous binder layer of Example 1, polyethylhexyl acrylate (poly(ethylhexyl acrylate)(MW=200,000 g / mol, average particle size (D)) instead of polymethyl methacrylate, 50 A wavelength of 350 nm was used.

[0161] Comparative Example 1 A safety-enhanced separation membrane (SRS) was manufactured using a dissolved PVDF-HFP binder and alumina, as described below.

[0162] Specifically, the solvent is acetone, to which PVDF-HFP (MW 400,000 g / mol, HFP 8 wt%) and average particle size (D 50 A slurry for forming a coating layer was prepared by adding 500nm alumina in a weight ratio of 1:4 and mixing it for about 2 hours using a bead mill mixer.

[0163] The coating layer forming slurry prepared above was applied to both sides of the same porous polymer substrate as in Example 1 using a bar coater, and a separation film was obtained by drying at room temperature (23°C) at a relative humidity of 45%.

[0164] The resulting separation membrane had porous coating layers formed on both sides of a porous polymer substrate (9 μm), with each porous coating layer having a thickness of 6 μm.

[0165] Comparative Example 2 Alumina (average particle size (D)) in water, which is the solvent. 50 )=500nm) and as an aqueous particle binder, PVDF-HFP (MW 400,000 g / mol, average particle size (D 50 A slurry was prepared by adding 250nm (HFP 5wt%) in a weight ratio of 95:5 and mixing it for 2 hours using a bead mill mixer.

[0166] The prepared slurry was applied to both sides of the same porous polymer substrate as in Example 1 using a bar coater, and then dried at 90°C to produce a separation membrane.

[0167] Comparative Example 3 The separation membrane was manufactured according to the same method as in Example 1, except that the first and second aqueous binder layers were not formed.

[0168] Comparative Example 4 A separation membrane was manufactured in the same manner as in Example 1, except that the first aqueous binder layer and the second aqueous binder layer were formed using a slurry for forming the first aqueous binder layer.

[0169] Comparative Example 5 A separation membrane was manufactured in the same manner as in Example 1, except that the first aqueous binder layer and the second aqueous binder layer were formed using a slurry for forming the second aqueous binder layer.

[0170] Comparative Example 6 Instead of using aluminum nitride as inorganic particles in the slurry for forming the first and second coating layers, alumina (average particle size (D) was used. 50 The first and second coating layers were formed according to the same method as in Example 1, except that a 500nm (500nm) was used.

[0171] Subsequently, a separation membrane was manufactured in the same manner as in Example 1, except that the first aqueous binder layer and the second aqueous binder layer were formed using a slurry for forming the second aqueous binder layer.

[0172] Comparative Example 7 Instead of using aluminum nitride as inorganic particles in the slurry for forming the first and second coating layers, alumina (average particle size (D) was used. 50 The separation membrane was manufactured according to the same method as in Example 1, except that a 500nm (500nm) was used.

[0173] Comparative Example 8 The slurry for forming the first coating layer and the slurry for forming the first aqueous binder layer prepared in Example 1 were mixed to prepare the aqueous slurry for forming the first porous coating layer.

[0174] The slurry for forming the second coating layer and the slurry for forming the second aqueous binder layer prepared in Example 1 were mixed to prepare an aqueous slurry for forming the second porous coating layer.

[0175] The first porous coating layer forming slurry was simultaneously coated onto one side of the same porous polymer substrate as in Example 1, and the second coating layer forming slurry was simultaneously coated onto the other side. The mixture was then thoroughly dried with hot air at 60°C to form the first and second porous coating layers, each 2.5 μm thick, thereby producing a separation membrane.

[0176] [Evaluation of physical properties of separation membranes] The physical properties of the separation membranes of Example 1 and Comparative Examples 1 to 8, which were manufactured as described above, were evaluated according to the following method.

[0177] Thermal shrinkage rate (%) The separation membrane to be evaluated was cut to a size of 50 mm x 50 mm, placed between sheets of A4 paper, and placed in a 120°C convection oven for 1 hour. After that, the thermal shrinkage rate in the mechanical direction (MD) and transverse direction (TD) was measured.

[0178] In this case, the thermal shrinkage rate (%) was calculated as [(initial length - length after heat treatment at 120°C / 1 hour) / (initial length)] × 100.

[0179] Dielectric breakdown voltage (V) The dielectric breakdown voltage was measured using an AC / DC / IR Hi-Pot tester.

[0180] Specifically, a 10x10cm piece of release PET was laminated onto the top and bottom of a 5x5cm piece of the separation membrane to be evaluated. The release surface of the release PET was ensured to be in contact with the separation membrane. The PET-laminated separation membrane was then hot-pressed for 10 seconds at a temperature of 70°C and a pressure of 5.2 MPa to produce a compressed separation membrane sample.

[0181] A compressed separation membrane sample was placed between aluminum fixtures (upper fixture diameter 30 mm, lower fixture 50 x 100 mm), and the voltage at which the fail condition (>0.5 mA, 3 sec) occurred was measured using a Hi-pot tester. The measurement conditions were set to DC, current 0.5 mA, and voltage boost 100 V / s (up to 3 kV). The measured values ​​were expressed as the average of 30 samples.

[0182] When the dielectric breakdown voltage is 1000V or higher, it is determined that the electrode assembly can be assembled without causing a short circuit.

[0183] Percentage increase in air permeability (%) The rate of increase in the permeability of the separation membrane was evaluated according to the following formula.

[0184] Permeability increase rate (%) = [(Permeability of manufactured separation membrane - Permeability of porous polymer substrate) / Permeability of porous polymer substrate] × 100

[0185] Air permeability (air permeability time, Gurley) was measured according to the ASTM D-2873 method. The Gurley value was measured using a Gurley type densometer (No. 158) manufactured by Toyoseiki Co., Ltd., in accordance with the Japanese Industrial Standard (JIS) Gurley measurement method. The air permeability value was calculated by passing 100 ml of air through a separation membrane at a pressure of 12.2 in H2O. 2This is expressed as the time (in seconds) it takes for air to pass through the cross-section, i.e., the permeability time.

[0186] Dry adhesion between the negative electrode and the separation membrane. A negative electrode slurry was obtained by adding natural graphite, SBR, CMC, and carbon black (by weight ratio of 90:2.5:2.5:5) to water, and the negative electrode slurry was spread on a copper thin film (thickness 20 μm) at a density of 5 mg / cm². 2 After coating with the specified loading amount, it was dried. Next, this was rolled at 90°C and 8.5 MPa, and cut into 60 mm (length) x 25 mm (width) pieces to prepare a standard negative electrode.

[0187] Next, the separation membrane to be evaluated was cut to a size of 70 mm (length) x 25 mm (width). After positioning it so that it was in contact with the prepared standard negative electrode and coating layer, the test specimen was prepared by laminating it using a press under the conditions of 60°C, 6.5 MPa, and 1 s.

[0188] The prepared test specimens were attached to a glass plate using double-sided tape, with the negative electrode facing the glass plate. The separation membrane portion of the test specimen was peeled off at a 180° angle at a speed of 300 mm / min at 25°C using an Instron UTM device, and the strength at this point was measured.

[0189] It was determined that unless a dry adhesive strength of 70 gf / 25 mm or higher was ensured, it would be impossible to manufacture electrode assemblies by electrode bonding.

[0190] Wet adhesion between electrodes and separation membrane After assembling the monocell as shown below, the electrolyte was injected to activate the electrode assembly and allow it to be impregnated with the electrolyte. Then, the electrode assembly was removed from the monocell, sampled in a 25 mm width, and fixed to the glass plate using double-sided tape so that the electrodes of the sampled electrode assembly faced the glass plate. The separation membrane portion of the test specimen was peeled off at a 90° angle at a speed of 200 mm / min at 25°C using an Instron UTM device, and the strength at this time was measured.

[0191] Wet adhesion strength was evaluated for both the adhesion between the positive electrode and the separation membrane and the negative electrode and separation membrane of the monocell. It was determined that if the wet adhesion strength was not 10 gf / 25 mm or higher, it would be impossible to manufacture the electrode assembly by electrode bonding.

[0192] Monocell was manufactured as follows:

[0193] 1) Manufacturing of the positive electrode Cathode active material (LiNi 0.8 Mn 0.1 Co 0.1 O2), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) were mixed with water in a weight ratio of 97.5:0.7:0.14:1.66 to prepare a slurry for the positive electrode active material layer with a concentration of 50 wt% of the remaining components after removing the water. Next, the slurry was applied to the surface of an aluminum thin film (10 μm thick) and dried to produce a positive electrode having a positive electrode active material layer (120 μm thick).

[0194] 2) Manufacturing of the negative electrode A slurry for the negative electrode active material layer was prepared by mixing graphite (a blend of natural and artificial graphite), a conductive material (carbon black), a dispersant, and a binder resin (a mixture of PVDF-HFP and PVDF) with water in a weight ratio of 97.5:0.7:0.14:1.66, with the remaining components after removing the water, at a concentration of 50 wt%. Next, the slurry was applied to the surface of a copper thin film (10 μm thick) and dried to produce a negative electrode having a negative electrode active material layer (120 μm thick).

[0195] 3) Lamination The separation membrane to be evaluated was interposed between the manufactured negative electrode and positive electrode and laminated, and an electrode assembly was obtained by performing a lamination process. The lamination process was carried out using a hot press at 70°C and 5.2 MPa for 10 seconds.

[0196] 4) Injection of electrolyte solution The electrolyte was prepared by dissolving 1.0 M lithium hexafluorophosphate (LiPF6) in an organic solvent consisting of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (EC / EMC / DEC mixed volume ratio = 3 / 4 / 3).

[0197] [Table 1]

[0198] Referring to the evaluation results in Table 1, it was confirmed that the separation membranes of Examples 1 and 2, which embody one example of the present invention, have superior physical properties compared to the separation membranes of Comparative Examples 1 to 8.

[0199] Specifically, the separation membrane in Comparative Example 1 showed a high thermal shrinkage rate and was found to be particularly poor in terms of dielectric breakdown voltage and air permeability increase rate. In Comparative Example 2, which lacked a water-based binder layer and used alumina as inorganic particles in the coating layer, the dielectric breakdown voltage was poor and poor adhesion to the electrode was confirmed in both the dry and wet states. In Comparative Example 3, which used aluminum nitride as inorganic particles in the coating layer, there was no water-based binder layer and poor adhesion to the electrode was confirmed in both the dry and wet states.

[0200] In Comparative Example 4, aluminum nitride was applied as inorganic particles to the coating layer, and a water-based binder layer was provided. However, fluorine-based particle binders were applied to both sides of the separation membrane, and it was confirmed that the adhesion to the negative electrode was poor in both the dry and wet states. In Comparative Example 5, similarly, acrylic-based particle binders were applied to both sides of the separation membrane, and it was confirmed that the adhesion to the positive electrode was poor. In Comparative Example 6, similar to Comparative Example 5, acrylic-based particle binders were applied to both sides, and alumina was applied as inorganic particles to the coating layer. This resulted in a lower dielectric breakdown voltage, and it was confirmed that the adhesion to the electrode was even worse in both the dry and wet states.

[0201] In Comparative Example 7, a fluorine-based particulate aqueous binder layer and an acrylic-based particulate aqueous binder layer were applied to both sides of the separation membrane, respectively. However, it was confirmed that the dielectric breakdown voltage was very poor due to the application of alumina as inorganic particles in the coating layer.

[0202] On the other hand, in Comparative Example 8, aluminum nitride was used as inorganic particles in the coating layer of the separation membrane, and a fluorine-based particle binder and an acrylic-based particle binder were applied to both sides of the separation membrane, respectively. However, it was confirmed that using a one-component slurry in which inorganic particles and particle binders were mixed together during coating layer formation resulted in degradation characteristics in terms of thermal shrinkage rate and electrode adhesion strength. [Explanation of Symbols]

[0203] 100: Separation membrane 1: Porous polymer base material 11: First coating layer 12: Second coating layer 111: Binder layer of the first river system 122: Second river system binder layer 110, 110': First particle type binder 120, 120': Second particle type binder

Claims

1. Porous polymer base material; A first coating layer formed on one side of the porous polymer substrate; A second coating layer formed on the other surface of the porous polymer substrate; A first aqueous binder layer formed on the surface of the first coating layer; and A second aqueous binder layer formed on the surface of the second coating layer; The first coating layer and the second coating layer each independently contain inorganic particles and a coating layer binder, the inorganic particles containing aluminum nitride (AlN), The first aqueous binder layer contains a first particle-type binder, and the second aqueous binder layer contains a second particle-type binder. A separation membrane for lithium secondary batteries, characterized in that the first particle-type binder and the second particle-type binder are different from each other, the first particle-type binder contains a fluorine-based binder, and the second particle-type binder contains an acrylic-based binder.

2. The first particle-type binder and the second particle-type binder each independently have an average particle size (D ５０ A separation membrane for a lithium secondary battery according to claim 1, characterized in that the thickness of the film is 0.05 to 0.5 μm.

3. The fluorine-based binder is polyvinylidene fluoride (PVDF); vinylidene fluoride monomer and trifluoroethylene (TrFE), tetrafluoroethylene (TFE), hexafluoropropylene (HFP), trichloroethylene (TrCE), tri A separation membrane for a lithium secondary battery according to claim 1, characterized by comprising a copolymer of one or more selected from chlorofluoroethylene (TCFE), chlorotrifluoroethylene (CTFE), polymethyl methacrylate (PMMA), and polyvinyl acetate (PVAc); or a mixture of two or more of these.

4. The aforementioned acrylic binders include polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, ethylhexyl acrylate, and methyl methacrylate. A separation membrane for a lithium secondary battery according to claim 1, characterized by comprising a copolymer of methyl methacrylate, a copolymer of butyl acrylate and methyl methacrylate, an ethyl acrylate-acrylic acid-N,N-dimethylacrylamide copolymer, an ethyl acrylate-acrylic acid-2-(dimethylamino)ethyl acrylate copolymer, an ethyl acrylate-acrylic acid-N,N-diethylacrylamide copolymer, an ethyl acrylate-acrylic acid-2-(diethylamino)ethyl acrylate copolymer, or a mixture of two or more of these.

5. The coating layer binder comprises an aqueous particulate binder. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the coating layer binder is the same as or different from the binder contained in the first aqueous binder layer and the second aqueous binder layer.

6. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the dry adhesion strength of the separation membrane for lithium secondary batteries to the electrodes is 70 gf / 25 mm or more.

7. The lithium secondary battery separation membrane according to claim 1, characterized in that the wet adhesion strength of the separation membrane for lithium secondary batteries to the electrodes is 10 gf / 25 mm or more.

8. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the adhesive strength between the porous polymer substrate and either the first coating layer or the second coating layer, or both, is 60 gf / 15 mm or more.

9. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the thickness of the first coating layer and the second coating layer are each independently 5 μm or less.

10. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the thickness of the first aqueous binder layer and the second aqueous binder layer are each independently 2 μm or less.

11. The separation membrane for lithium secondary batteries according to claim 1, characterized in that the thickness of the porous polymer substrate is 15 μm or less.

12. In a lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separation membrane for a lithium secondary battery interposed between the positive electrode and the negative electrode, A lithium secondary battery, characterized in that the separation membrane for the lithium secondary battery is the separation membrane for the lithium secondary battery described in any one of claims 1 to 11.

Images