Separator for electrochemical device, and manufacturing method thereof

Abstract

A separator according to the present invention comprises a porous polymer substrate, an adhesive layer, and a heat-resistant layer, wherein the adhesive layer includes an acrylic binder polymer having a swelling degree of 50% or greater. The separator can ensure sufficient peel strength while being thin.

Description

Separator for electrochemical devices and method for manufacturing the same

[0001] The present invention relates to a separator for an electrochemical device and a method for manufacturing the same.

[0002] This application claims priority to Korean Application No. 10-2024-0091290, filed July 10, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] Interest in energy storage technology has been growing steadily. As its applications expand to include energy storage for mobile phones, camcorders, laptops, and even electric vehicles, research and development efforts for electrochemical devices are becoming increasingly concrete. Electrochemical devices are receiving the most attention in this regard, and within this field, the development of rechargeable secondary batteries is a particular focus. Recent research and development efforts are focused on novel electrode and battery designs to improve capacity density and specific energy.

[0004] These electrochemical devices comprise an electrode assembly with a separator interposed between the positive and negative electrodes, housed within a battery case. This separator prevents short circuits caused by contact between the positive and negative electrodes, while providing a path for the electrolyte to flow between the two electrodes. Therefore, it is crucial that the electrode assembly structure, consisting of the stacked positive electrode, separator, and negative electrode, be maintained even after immersion in an electrolyte.

[0005] To improve the safety of electrochemical devices, attempts have been made to apply a separator comprising a heat-resistant layer containing ceramic on at least one surface of a porous polymer substrate. However, when the heat-resistant layer is formed thinly to achieve a thinner separator, the adhesive strength between the porous polymer substrate and the heat-resistant layer weakens, leading to peeling.

[0006] The problem to be solved by the present invention is to provide a separator having improved peel strength while ensuring a thin thickness.

[0007] In one aspect of the present invention, the following embodiments provide a separator, an electrochemical device, and a method for manufacturing a separator.

[0008] The separation membrane according to the first embodiment is

[0009] A porous polymer substrate; and a porous coating layer,

[0010] The porous coating layer includes an adhesive layer positioned on at least one surface of the porous polymer substrate; and a heat-resistant layer positioned on one surface of the adhesive layer.

[0011] The adhesive layer comprises a first binder polymer,

[0012] The above heat-resistant layer includes inorganic particles and a second binder polymer,

[0013] The above first binder polymer comprises an acrylic polymer,

[0014] The swelling ratio of the above acrylic polymer is characterized by being 50% or more.

[0015] The second embodiment is, in the first embodiment,

[0016] The swelling degree of the above acrylic polymer may be 60% or more.

[0017] The third embodiment is, in the first embodiment or the second embodiment,

[0018] The swelling degree of the above acrylic polymer can be measured by the following equation 1.

[0019] (Formula 1) Swelling (%) = {(W1-W0) / W0}×100

[0020] In the above equation 1, W0 is the initial mass measured at 25°C of the film manufactured from the binder polymer, and W1 is the mass measured at 25°C after the manufactured binder polymer film is impregnated in dimethyl carbonate and stored at 60°C for 48 hours.

[0021] The fourth embodiment is, in any one of the first to third embodiments,

[0022] The above carbonate solvent may include dimethyl carbonate.

[0023] The fifth embodiment is, in any one of the first to fourth embodiments,

[0024] The above acrylic polymer is crosslinked, and the degree of crosslinking may be from 0.01% to 80%.

[0025] The sixth embodiment is, in any one of the first to fifth embodiments,

[0026] The above acrylic polymer may include poly(methylmethacrylate), poly(ethylhexyl acrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexyl acrylate and methyl methacrylate, a copolymer of butylacrylate 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 thereof. there is.

[0027] The seventh embodiment is, in any one of the first to sixth embodiments,

[0028] The peel strength between the porous polymer substrate and the porous coating layer may be 50 gf / 15 mm or more.

[0029] The eighth embodiment is, in any one of the first to seventh embodiments,

[0030] The above adhesive layer may not contain inorganic particles.

[0031] The electrochemical device according to the 9th embodiment is:

[0032] Comprising an anode, a cathode, and a separator interposed between the anode and the cathode,

[0033] The above separation membrane is characterized by being a separation membrane according to any one of the first to eighth embodiments.

[0034] The method for manufacturing a separation membrane according to the 10th embodiment is as follows:

[0035] Step of preparing a porous polymer substrate;

[0036] A step of preparing a slurry for forming an adhesive layer including a first binder polymer and a first aqueous solvent, and applying and drying the slurry for forming an adhesive layer on at least one surface of the porous polymer substrate to form an adhesive layer;

[0037] A step of preparing a slurry for forming a heat-resistant layer including inorganic particles, a second binder polymer, a second aqueous solvent, and an organic solvent, and applying and drying the slurry for forming a heat-resistant layer on one surface of the adhesive layer to form a heat-resistant layer;

[0038] The above first binder polymer comprises an acrylic polymer,

[0039] The swelling ratio of the above acrylic polymer is characterized by being 50% or more.

[0040] The 11th implementation example is, in the 10th implementation example,

[0041] The above organic solvent may include a carbonate system.

[0042] The 12th embodiment is, in the 10th embodiment or the 11th embodiment,

[0043] The organic solvent may include dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and ethylmethyl carbonate or mixtures thereof.

[0044] The 13th embodiment is any one of the 10th to 12th embodiments,

[0045] The second aqueous solvent and the organic solvent can be mixed in a volume ratio of 95:5 to 80:20.

[0046] A separator according to one aspect of the present invention may have a thin thickness. In addition, the separation strength between the porous coating layer and the porous polymer substrate is excellent.

[0047] Hereinafter, the present invention will be described in detail with reference to the drawings. Terms and words used in this specification and claims should not be construed as limited to their conventional or dictionary meanings. Based on the principle that the inventor can appropriately define the concept of a term to best explain his or her invention, they should be interpreted in the sense and concept consistent with the technical spirit of the present invention.

[0048] Accordingly, the embodiments described in this specification and the configurations described in the drawings are only the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention. Therefore, it should be understood that there may be various equivalents and modified examples that can replace them at the time of filing this application.

[0049] Additionally, throughout the specification, whenever a part is said to "include," "comprise," "have," or "have" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0050] In addition, the terms 'about', 'substantially', etc. used throughout this specification are used in the sense of or near to the numerical values ​​when manufacturing and material tolerances inherent to the meanings stated are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure where exact or absolute values ​​are mentioned to aid understanding of this specification.

[0051] Throughout this specification, references to 'A and / or B' mean 'A or B or both.'

[0052] Unless otherwise specified throughout this specification, temperature refers to Celsius temperature, and the unit is ℃.

[0053]

[0054] The first aspect of the present invention relates to a separation membrane.

[0055] According to one aspect of the present invention, a separation membrane is provided.

[0056] A porous polymer substrate; and a porous coating layer,

[0057] The porous coating layer includes an adhesive layer positioned on at least one surface of the porous polymer substrate; and a heat-resistant layer positioned on one surface of the adhesive layer.

[0058] The adhesive layer comprises a first binder polymer,

[0059] The above heat-resistant layer includes inorganic particles and a second binder polymer,

[0060] The above first binder polymer comprises an acrylic polymer,

[0061] It is characterized in that the swelling ratio of the above acrylic polymer is 50% or more.

[0062]

[0063] In the present invention, the swelling degree can be measured by the following equation 1:

[0064] (Formula 1) Swelling degree (%) = {(W1-W0) / W0}Х100

[0065] In the above equation 1, W0 is the initial mass of the film manufactured from an acrylic polymer measured at room temperature (approximately 25°C), and W1 is the mass of the film measured at room temperature (approximately 25°C) after the manufactured acrylic polymer film is impregnated in dimethyl carbonate and stored at 60°C for 48 hours.

[0066]

[0067] The separator according to the present invention includes an acrylic binder having a swelling degree of 50% or more in the adhesive layer. That is, the mass after swelling may be 150% or more of the initial mass of the acrylic binder before swelling. The acrylic binder may be swollen by a solvent included in the slurry for forming a heat-resistant layer when the slurry for forming a heat-resistant layer is applied. Since the acrylic binder must be able to sufficiently swell only with the solvent included in the slurry for forming a heat-resistant layer, the swelling degree must be 50% or more. A sufficiently swollen acrylic polymer can strengthen the adhesive force between the porous polymer substrate and the heat-resistant layer.

[0068]

[0069] Hereinafter, the separation membrane according to the present invention will be described in detail.

[0070] A separator according to the present invention comprises a porous coating layer on at least one surface of a porous polymer substrate. In addition, the porous coating layer comprises an adhesive layer positioned on at least one surface of the porous polymer substrate, and a heat-resistant layer positioned on one surface of the adhesive layer.

[0071]

[0072] porous polymer substrate

[0073] In one embodiment of the present invention, the porous polymer substrate can be used without any particular limitation as long as it can be commonly used as a material for a separator for an electrochemical device. Non-limiting examples of polymer materials used in the porous polymer substrate include olefin polymers, ethylene terephthalate polymers, butylene terephthalate polymers, acetal polymers, amide polymers, carbonate polymers, imide polymers, ether ether ketone polymers, ether sulfone polymers, phenylene oxide polymers, phenylene sulfide polymers, ethylene naphthalene polymers, and the like.

[0074] In addition, the porous polymer substrate may be a nonwoven fabric or porous polymer film formed of the polymer material described above, or a laminate of two or more thereof. Specifically, the porous polymer substrate may be any one of the following a) to e).

[0075] a) A porous film formed by melting and extruding a polymer material,

[0076] b) A multilayer film in which two or more layers of the porous film of a) above are laminated,

[0077] c) Nonwoven web manufactured by accumulating filaments obtained by melting / spinning polymer materials;

[0078] d) A multilayer film in which two or more layers of the nonwoven web of c) above are laminated,

[0079] e) A porous membrane having a multilayer structure comprising two or more of the above a) to d).

[0080]

[0081] The above porous polymer substrate can be manufactured by forming pores through a conventional method known in the art, such as a wet method using a solvent, diluent, or pore-forming agent, or a dry method using a stretching method, to secure excellent air permeability and porosity from the above-mentioned material.

[0082]

[0083] In one embodiment of the present invention, the thickness of the porous polymer substrate is not particularly limited, but may be 1 μm to 100 μm, or 1 μm to 30 μm. When the thickness of the porous polymer substrate is within the aforementioned range, it is possible to prevent the problem of the separator being easily damaged during battery use, while also making it easy to secure energy density.

[0084] Meanwhile, the average pore size and porosity of the porous polymer substrate are not particularly limited as long as they are suitable for use in electrochemical devices, and the average pore size may be 0.01 ㎛ to 50 ㎛, or 0.1 ㎛ to 20 ㎛, and the porosity may be 5% to 95%. When the pore size and porosity are within the above-mentioned ranges, it may be easy to prevent the porous polymer substrate from acting as a resistor, and it may be easy to maintain the mechanical properties of the porous polymer substrate.

[0085] The average pore size and porosity of the above porous polymer substrate can be measured by the BET 6-point method using a scanning electron microscope (SEM) image, a mercury porosimeter, a capillary flow porometer, or a porosimetry analyzer (Bell Japan Inc, Belsorp-II mini) using a nitrogen gas adsorption flow method.

[0086]

[0087] adhesive layer

[0088] The adhesive layer according to the present invention comprises a first binder polymer, wherein the first binder polymer comprises an acrylic polymer, and the acrylic polymer is characterized in that it has a swelling degree of 50% or more.

[0089]

[0090] In one embodiment of the present invention, the swelling degree of the acrylic binder may be 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more. In addition, the swelling degree of the acrylic binder may be 400% or less. When the swelling degree of the acrylic binder falls within the above range, the peel strength between the porous polymer substrate and the porous coating layer can be significantly improved.

[0091]

[0092] In one embodiment of the present invention, the weight average molecular weight of the acrylic binder polymer may be 10,000 to 1,000,000. When the weight average molecular weight of the acrylic binder polymer falls within the above range, it may have a sufficient swelling degree.

[0093]

[0094] In one embodiment of the present invention, the weight average molecular weight of the acrylic binder polymer can be determined by measuring the weight average molecular weight (Mw) and number average molecular weight (Mn) of 1 g of the acrylic polymer solution using gel permeation chromatography (GPC: PL GPC220, Agilent Technologies) under the following conditions, and calculating the molecular weight distribution.

[0095] Column: PLmixed B Х 2,

[0096] Solvent: DMF / 0.05 M LiBr (0.45㎛ Filtered),

[0097] Flow rate: 1.0 ㎖ / min,

[0098] Sample concentration: 4.0 mg / ml,

[0099] Injection volume: 100 ㎕,

[0100] Column temperature: 65℃

[0101] Detector: Waters RI Detector, Standard: PS)

[0102]

[0103] In one embodiment of the invention, the acrylic binder polymer is poly(methylmethacrylate), poly(ethylhexyl acrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexyl acrylate and methyl methacrylate, a copolymer of butylacrylate 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 It may include a copolymer or a mixture of two or more thereof, and preferably may include polymethyl methacrylate.

[0104] The acrylic binder polymer may include a hydrophilic functional group such as an OH group, a CO group, a COH group, and / or a COOH group. When the acrylic binder includes a hydrophilic functional group, it can swell more smoothly. In addition, the acrylic binder polymer may include an acrylic copolymer polymer including a hydrophilic functional group such as an OH group, a CO group, a COH group, and / or a COOH group. Acrylic bar

[0105]

[0106] In one embodiment of the present invention, the first binder polymer may be non-crosslinked or may be crosslinked.

[0107] When the first binder polymer is crosslinked, the degree of crosslinking of the first binder polymer may be 0.01% or more, 0.1% or more, 1% or more, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55% or more, 60% or more, and may be 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, or 20% or less.

[0108] The degree of crosslinking of the first binder polymer may vary depending on the properties of the binder polymer. For example, if the first binder polymer has few hydrophilic functional groups, it may be applied without crosslinking or with a low degree of crosslinking. Furthermore, if the first binder polymer has many hydrophilic functional groups, it may be applied with a high degree of crosslinking. In other words, by controlling the degree of crosslinking of the first binder polymer within the above range, a swelling degree of 50% or more can be secured.

[0109] The above cross-linking degree can be calculated by manufacturing a film with the first binder polymer, measuring the initial weight of the film, immersing it in a decalin solution at 135°C according to ASTM D 2765, boiling it for 4 hours, and measuring the remaining dry weight, and then calculating the ratio of the remaining dry weight to the initial weight.

[0110]

[0111] In one embodiment of the present invention, the adhesive layer may contain the acrylic polymer in an amount of 80 wt% or more, 85 wt% or more, 90 wt% or more, 95 wt% or more, 97 wt% or more, 98 wt% or more, or 99 wt% or more, based on a total of 100 wt%, and may contain the acrylic polymer in an amount of substantially 100 wt%. That is, the adhesive layer may be composed of only the acrylic polymer. However, the present invention is not limited thereto, and the adhesive layer may further contain a binder polymer commonly used in the art in addition to the acrylic polymer, if necessary.

[0112]

[0113] In one embodiment of the present invention, the adhesive layer may not include separate inorganic particles and may only include a binder polymer.

[0114]

[0115] heat-resistant layer

[0116] The heat-resistant layer according to the present invention includes inorganic particles and a second binder polymer.

[0117]

[0118] In one embodiment of the present invention, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the applied electrochemical device (e.g., 0 to 5 V based on Li / Li+). In particular, when inorganic particles having a high dielectric constant are used, they can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0119] For the reasons mentioned above, in one embodiment of the present invention, the inorganic particles may include high-dielectric constant inorganic particles having a dielectric constant of 5 or more, preferably 10 or more. Non-limiting examples of inorganic particles having a dielectric constant of 5 or more include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT, 0 <x<1, 0<y<1), Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3(PMN-PT), hafnia(HfO2), SrTiO3, SnO2, CeO2, MgO, Mg(OH)2, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, AlOOH, Al(OH)3, SiC, TiO2 or a mixture thereof. In addition, as the inorganic particles, inorganic particles having lithium ion transfer capability, i.e., inorganic particles containing lithium element but having the function of transferring lithium ions without storing lithium, can be used. Non-limiting examples of inorganic particles having lithium ion transfer capability include lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 <x<2, 0<y<3), 리튬알루미늄티타늄포스페이트(Li x Al y Ti z (PO4)3, 0 <x<2, 0<y<1, 0<z<3), 14Li2O-9Al2O3-38TiO2-39P2O5등과 같은 (LiAlTiP) x O y Series glass (0 <x<4, 0<y<13), 리튬란탄티타네이트(Li x La y TiO3, 0 <x<2, 0<y<3), Li 3.25 Ge 0.25 P 0.75 Lithium germanium thiophosphate (Li) such as S4 x Ge y P z S w, 0 <x<4, 0<y<1, 0<z<1, 0<w< 5), Li3N 등과 같은 리튬나이트라이드(Li x N y , 0 <x<4, 0<y<2), Li3PO4-Li2S-SiS2등과 같은 SiS2계열 glass(Li x Si y S z , 0 <x<3, 0<y<2, 0<z<4), LiI-Li2S-P2S5등과 같은 P2S5계열 glass(Li x P y S z , 0 <x< 3, 0<y<3, 0<z<7), 또는 이들의 혼합물 등이 있다.

[0120]

[0121] In one embodiment of the present invention, the average particle diameter of the inorganic particles may be 0.01 μm to 1.5 μm. When the average particle diameter of the inorganic particles satisfies the above-described range, the formation of an inorganic hybrid porous layer having a uniform thickness and appropriate porosity can be facilitated, and the dispersibility of the inorganic particles can be good and provide a desired energy density.

[0122] At this time, the average particle diameter of the above-mentioned inorganic particles is D 50 It means entry, "D 50 "Particle size" means the particle size at the 50% point of the cumulative distribution of the number of particles according to particle size. The particle size can be measured using a laser diffraction method. Specifically, after the powder to be measured is dispersed in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and the particle size distribution is calculated by measuring the difference in the diffraction pattern according to the particle size when the particles pass through the laser beam. By calculating the particle diameter at the point where the cumulative distribution of the number of particles according to particle size in the measuring device becomes 50%, the D50 particle size can be measured.

[0123]

[0124] In one embodiment of the present invention, with respect to the total 100 wt% of the heat-resistant layer, the inorganic particles may be included in an amount of 60 to 95 wt%, 65 to 95 wt%, 70 to 95 wt%, or 75 to 95 wt%. When the content range of the inorganic particles falls within the above range, the voids formed between the inorganic particles can be sufficiently secured, thereby securing the porosity of the heat-resistant layer, and the heat-resistant performance of the separator can be sufficiently secured.

[0125]

[0126] In one embodiment of the present invention, the second binder polymer may be a binder polymer commonly used in the art. Non-limiting examples of the second binder polymer include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cyanoethylpullulan, and cyanoethylpolyvinyl alcohol. It may be any one polymer resin selected from the group consisting of (cyanoethylpolyvinylalcohol), cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxyl methyl cellulose, or a mixture of two or more thereof, but is not particularly limited thereto.

[0127]

[0128] In one embodiment of the present invention, the swelling degree of the second binder polymer may be 30% or less, 20% or less, 10% or less, 5% or less, or 3% or less. The swelling degree of the second binder polymer may be measured by the same method as the method for measuring the swelling degree of the first binder polymer. Since the swelling degree of the second binder polymer is low in the slurry corresponding to the above range, stability can be ensured when coating the slurry. In addition, since sufficient porosity can be secured in the heat-resistant layer, low resistance can be ensured.

[0129]

[0130] In one embodiment of the present invention, the heat-resistant layer may further include an additive such as a dispersant and / or a thickener. For example, the additive may include cyanoethyl polyvinylalcohol (PVA-CN), citric acid, hydroxy ethyl cellulose (HEC), hydroxy propyl cellulose (HPC), ethylhydroxy ethyl cellulose (EHEC), methyl cellulose (MC), carboxymethyl cellulose (CMC), hydroxyalkyl methyl cellulose, or two or more thereof.

[0131]

[0132] In one embodiment of the present invention, the thickness of the heat-resistant layer may be 0.5 µm to 10 µm, 0.5 µm to 5 µm, or 0.5 µm to 3 µm. When the thickness of the heat-resistant layer falls within the above range, the separator can secure excellent heat-resistant performance while having a sufficiently thin thickness.

[0133]

[0134] In one embodiment of the present invention, the peel strength between the porous polymer substrate and the porous coating layer may be 50 gf / 15 mm or more, 60 gf / 15 mm or more, 70 gf / 15 mm or more, 80 gf / 15 mm or more, 90 gf / 15 mm or more, or 100 gf / 15 mm or more. When the peel strength falls within the above range, the separator is not peeled during the manufacture and operation of the secondary battery, thereby ensuring the safety of the secondary battery.

[0135] The above peel strength can be measured by the following method.

[0136] Cut the separator to 15 mm Х 100 mm in size. Attach double-sided adhesive tape to a glass plate and attach it so that the porous coating layer surface of the prepared separator adheres to the adhesive tape. After that, attach the end of the attached separator to the UTM device (LLOYD Instrument LF Plus) and apply force at a measurement speed of 300 mm / min at a 180-degree angle to measure the force required to peel the porous coating layer from the porous polymer substrate.

[0137]

[0138] The second aspect of the present invention relates to an electrochemical device.

[0139] An electrochemical device according to one aspect of the present invention comprises an anode, a cathode, and a separator interposed between the anode and the cathode,

[0140] The above separation membrane is characterized as being a separation membrane according to one aspect of the present invention.

[0141]

[0142] In one embodiment of the present invention, the electrochemical device includes all devices that perform an electrochemical reaction, and specific examples thereof include capacitors such as all types of primary and secondary batteries, fuel cells, solar cells, or supercapacitor devices. In particular, the electrochemical device may be a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, a lithium sulfur battery, or a lithium ion polymer secondary battery.

[0143]

[0144] The electrode to be applied together with the separator for the electrochemical device of the present invention is not particularly limited, and can be manufactured in a form in which an electrode active material layer including an electrode active material, a conductive material, and a binder is bonded to an electrode current collector according to a conventional method known in the art.

[0145] Non-limiting examples of the positive electrode active material among the above electrode active materials include layered compounds such as lithium cobalt composite oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; chemical formula Li 1+x Mn 2-x Lithium manganese oxides such as O4 (where x = 0~0.33), LiMnO3, LiMn2O3, LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O5, LiV3O4, V2O5, Cu2V2O7; chemical formula LiNi 1-x M x Ni-site type lithium nickel oxide represented by O2 (wherein, M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); chemical formula LiMn 2-x M xLithium manganese composite oxides expressed as O2 (wherein, M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li2Mn3MO5 (wherein, M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which a portion of the chemical formula Li is replaced with an alkaline earth metal ion; disulfide compounds; Fe2(MoO4)3, etc., but are not limited thereto.

[0146] Non-limiting examples of the negative electrode active material include conventional negative electrode active materials that can be used in the negative electrode of conventional electrochemical devices, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons, and lithium adsorbents, etc. can be used.

[0147] Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof, and non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, or copper alloys, or combinations thereof.

[0148] In one embodiment of the present invention, the conductive material used in the negative electrode and the positive electrode can be typically added in an amount of 1 wt% to 30 wt% based on the total weight of each active material layer. The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, server black; conductive fibers such as carbon fiber or metal fiber; fluorinated carbon; metal powders such as aluminum or nickel powder; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0149]

[0150] In one embodiment of the present invention, the binder polymer used in the negative electrode and the positive electrode is a component that assists in the bonding of the active material and the conductive material and the bonding to the current collector, and can typically be added in an amount of 1 wt% to 30 wt% based on the total weight of each active material layer. Examples of such binders include polyvinylidene fluoride (PVdF), polyacrylic acid (PAA), polyvinyl alcohol, carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-dienhe polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers, and the like.

[0151]

[0152] In one embodiment of the present invention, the electrochemical device comprises an electrolyte, which may comprise an organic solvent and a lithium salt. In addition, an organic solid electrolyte or an inorganic solid electrolyte may be used as the electrolyte.

[0153] As the organic solvent, for example, an aprotic organic solvent such as N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-ibidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, ethyl propionate, etc. can be used.

[0154] The above lithium salt is a substance that is easily dissolved in the organic solvent, for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium 4-phenylborate, imide, etc. can be used.

[0155] In addition, for the purpose of improving the charge / discharge characteristics, flame retardancy, etc. of the electrolyte, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. may be added. In some cases, in order to provide incombustibility, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoroethylene may be further included, and carbon dioxide gas may be further included to improve high-temperature storage characteristics.

[0156] As the organic solid electrolyte, for example, polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ionic dissociation groups, etc. can be used.

[0157] As the above inorganic solid electrolyte, for example, nitrides, halides, sulfates, etc. of Li, such as Li3N, LiI, Li5NI2, Li3N-LiI-LiOH, LiSiO4, LiSiO4-LiI-LiOH, Li2SiS3, Li4SiO4, Li4SiO4-LiI-LiOH, Li3PO4-Li2S-SiS2, etc. can be used.

[0158] The above electrolyte injection can be performed at an appropriate stage during the battery manufacturing process, depending on the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.

[0159]

[0160] The third aspect of the present invention relates to a method for manufacturing a separation membrane.

[0161] A method for manufacturing a separation membrane according to one aspect of the present invention,

[0162] Step of preparing a porous polymer substrate;

[0163] A step of preparing a slurry for forming an adhesive layer including a first binder polymer and a first aqueous solvent, and applying and drying the slurry for forming a first coating layer on at least one surface of the porous polymer substrate to form an adhesive layer;

[0164] A step of preparing a slurry for forming a heat-resistant layer including inorganic particles, a second binder polymer, a second aqueous solvent, and an organic solvent, and applying and drying the slurry for forming a heat-resistant layer on one surface of the adhesive layer to form a heat-resistant layer;

[0165] The above first binder polymer comprises an acrylic polymer,

[0166] The swelling ratio of the above acrylic polymer is characterized by being 50% or more.

[0167]

[0168] After forming an adhesive layer on one or both sides of a porous polymer substrate, a slurry for forming a heat-resistant layer is applied. At this time, the acrylic polymer included in the adhesive layer can absorb the organic solvent included in the slurry for forming a heat-resistant layer and swell by 50% or more.

[0169]

[0170] In one embodiment of the present invention, the organic solvent comprises a carbonate solvent. For example, the organic solvent may comprise at least one of linear carbonates composed of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and ethylmethyl carbonate; and / or at least one of cyclic carbonates composed of ethylene carbonate, propylene carbonate, and butylene carbonate; or a mixture thereof. Preferably, the organic solvent may be dimethyl carbonate.

[0171]

[0172] In one embodiment of the present invention, the second aqueous solvent and the organic solvent in the slurry for forming a heat-resistant layer may be mixed in a volume ratio of 95:5 to 80:20, 95:5 to 90:10, or 90:10 to 80:20. When the second aqueous solvent and the organic solvent are mixed in the above-mentioned range of contents, when the slurry for forming a heat-resistant layer is applied to one surface of the adhesive layer, the first binder polymer included in the adhesive layer can sufficiently absorb the organic solvent and swell.

[0173]

[0174] Hereinafter, the present invention will be described in more detail through examples, but the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited to these examples.

[0175]

[0176] Example 1

[0177] A 9 ㎛ thick polyethylene film was prepared as a porous polymer substrate.

[0178] A slurry for forming an adhesive layer with a solid content of 10% was prepared by adding polymethyl methacrylate (PMMA) with a crosslinking degree of 60% as a first binder polymer to water, and the slurry was applied / dried on both sides of the porous polymer substrate to form an adhesive layer.

[0179] Water and dimethyl carbonate were mixed in a volume ratio of 90:10, and Al2O3 was added as an inorganic particle and PVDF-HFP as a second binder polymer to prepare a slurry for forming a heat-resistant layer with a solid content of 35%. Then, the slurry for forming a heat-resistant layer was applied and dried on one side of the adhesive layer to form a heat-resistant layer, thereby manufacturing a separator. The thickness of the adhesive layer was measured to be 0.5 μm, and the thickness of the heat-resistant layer was measured to be 1.5 μm.

[0180] At this time, the first binder polymer, PMMA, was used having a swelling ratio of 60% with respect to dimethyl carbonate.

[0181]

[0182] Example 2

[0183] A separation membrane was manufactured in the same manner as in Example 1, except that polymethyl methacrylate (PMMA) with a crosslinking degree of 10% was used as the first binder polymer.

[0184] At this time, the swelling degree of the first binder polymer was calculated to be 90%.

[0185]

[0186] Comparative Example 1

[0187] A separator was manufactured in the same manner as in Example 1, except that the slurry for forming a heat-resistant layer was applied and dried directly on both sides of the porous polymer substrate without forming an adhesive layer.

[0188]

[0189] Comparative Example 2

[0190] A membrane was manufactured in the same manner as in Example 1, except that polyacrylonitrile having a crosslinking degree of 60% and a swelling ratio in dimethyl carbonate of 30% was used as the first binder polymer.

[0191]

[0192] Comparative Example 3

[0193] A membrane was manufactured in the same manner as in Example 1, except that PVDF-HFP having a crosslinking degree of 85% and a swelling ratio of 130% in dimethyl carbonate was used as the first binder polymer.

[0194]

[0195] Comparative Example 4

[0196] A membrane was manufactured in the same manner as in Example 1, except that polyvinylpyrrolidone (PVP) was used as the first binder polymer.

[0197] Since the above polyvinylpyrrolidone is a binder polymer manufactured by solution polymerization, it was not possible to compare the swelling degree with that of an acrylic binder polymer manufactured by emulsion polymerization.

[0198]

[0199] Comparative Example 5

[0200] A separation membrane was manufactured in the same manner as in Example 1, except that polymethyl methacrylate (PMMA) with a crosslinking degree of 10% was used as the first binder polymer.

[0201] At this time, the swelling degree of the first binder polymer was calculated to be 45%.

[0202]

[0203] Comparative Example 6

[0204] A separator was manufactured in the same manner as in Example 1, except that the slurry for forming a heat-resistant layer was first applied and dried on both sides of a porous polymer substrate to form a heat-resistant layer, and then the slurry for forming an adhesive layer was applied and dried on one side of the heat-resistant layer to form an adhesive layer. That is, the order of laminating the adhesive layer and the heat-resistant layer was reversed from that in Example 1.

[0205]

[0206] Swelling measurement method

[0207] In the above examples / comparative examples, the swelling degree was calculated by measuring the initial mass (W0) of the film manufactured with the binder polymer, impregnating it in dimethyl carbonate, storing it at 60°C for 48 hours, and then measuring the mass (W1), and substituting it into Equation 1 below.

[0208] (Formula 1) Swelling degree (%) = {(W1-W0) / W0}Х100

[0209]

[0210] Cross-linking degree measurement method

[0211] In the above examples / comparative examples, the degree of crosslinking was calculated by manufacturing a film with the first binder polymer, measuring the initial weight of the film, immersing it in a decalin solution at 135°C according to ASTM D 2765, boiling it for 4 hours, and measuring the remaining dry weight, and then calculating the ratio of the remaining dry weight to the initial weight.

[0212]

[0213] How to measure thickness

[0214] In the above examples / comparative examples, the thickness of the adhesive layer and the heat-resistant layer was measured using a thickness measuring device (Mitutoyo).

[0215]

[0216] Experimental Example 1: Peel strength measurement

[0217] For the membranes manufactured in the examples and comparative examples, the peel strength between the porous polymer substrate and the porous coating layer was measured, and the results are shown in Table 1 below.

[0218] Specifically, the separators manufactured in Examples 1 to 2 and Comparative Examples 1 to 4 were cut to a size of 15 mm Х 100 mm. Double-sided adhesive tape was attached on a glass plate, and the porous coating layer surface of the prepared separator was attached so that it adhered to the adhesive tape. Thereafter, the end of the bonded separator was mounted on a UTM device (LLOYD Instrument LF Plus), and a force was applied at a measuring speed of 300 mm / min at an angle of 180 degrees to measure the force required for the porous coating layer and the porous polymer substrate to be peeled off.

[0219]

[0220] Presence of adhesive layer Type of first binder polymer Swelling degree of first binder polymer (%) Peel strength (gf / 15mm) Example 1 ○ Acrylic 60% 109 Example 2 ○ Acrylic 90% 121 Comparative example 1 × - - 32 Comparative example 2 ○ Acrylic 30% 45 Comparative example 3 ○ PVDF 30% 41 Comparative example 4 ○ PVP - 10 Comparative example 5 ○ Acrylic 45% 55 Comparative example 6 ○ Acrylic 60% 40

[0221] Referring to Table 1 above, it can be confirmed that the separator according to the present invention has significantly superior peel strength compared to the separator according to the comparative example.

[0222] Specifically, it was confirmed that the separator according to Comparative Example 1 had a weak peel strength because it did not form an adhesive layer. In addition, it was confirmed that the separators according to Comparative Examples 2 and 5 did not sufficiently improve the peel strength because, although an acrylic binder polymer was applied, the swelling degree was low at 30% or 45%.

[0223] In the case of Comparative Example 3 using a PVDF binder, since the PVDF binder polymer is a crystalline polymer, unlike an acrylic binder, it is difficult for the electrolyte to penetrate, and thus a high swelling value cannot be achieved, and accordingly, sufficient peel strength cannot be secured.

[0224] In Comparative Example 4, where a PVP-based binder polymer was applied, a very low peel strength was observed. This is because, since the PVP-based binder polymer is soluble in organic solvents, the PVP-based binder polymer dissolved in the dimethyl carbonate contained in the slurry for forming a heat-resistant layer when the slurry for forming a heat-resistant layer was applied. On the other hand, since the PVP-based binder polymer is a binder polymer manufactured by solution polymerization, it is judged that the swelling degree cannot be compared on the same level with that of an acrylic binder polymer manufactured by emulsion polymerization.

[0225] Comparative Example 6 formed a heat-resistant layer on both sides of a porous polymer substrate, and then formed an adhesive layer on the heat-resistant layer. The positions of the heat-resistant layer / adhesive layer were reversed compared to Example 1. Since the heat-resistant layer was formed before the adhesive layer, the binder polymer of the adhesive layer did not swell sufficiently, and thus sufficient peel strength could not be secured.

[0226]

[0227] As described above, although the present invention has been described by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical idea of ​​the present invention and the equivalent scope of the patent claims to be described below by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. A porous polymer substrate; and a porous coating layer, The porous coating layer includes an adhesive layer positioned on at least one surface of the porous polymer substrate; and a heat-resistant layer positioned on one surface of the adhesive layer. The adhesive layer comprises a first binder polymer, The above heat-resistant layer includes inorganic particles and a second binder polymer, The above first binder polymer comprises an acrylic polymer, The swelling ratio of the above acrylic polymer is characterized by being 50% or more.

2. In paragraph 1, A separation membrane characterized in that the swelling degree of the above acrylic polymer is 60% or more.

3. In paragraph 1, A membrane characterized in that the swelling degree of the acrylic polymer is measured by the following equation 1: (Formula 1) Swelling degree (%) = {(W1-W0) / W0}Х100 In the above equation 1, W0 is the initial mass measured at 25°C of the film manufactured from the binder polymer, and W1 is the mass measured at 25°C after the manufactured binder polymer film is impregnated in dimethyl carbonate and stored at 60°C for 48 hours.

4. In paragraph 3, A separation membrane characterized in that the carbonate solvent comprises dimethyl carbonate.

5. In paragraph 1, A separation membrane characterized in that the above acrylic polymer is crosslinked and has a crosslinking degree of 0.01% to 80%.

6. In paragraph 1, The above acrylic polymer includes poly(methylmethacrylate), poly(ethylhexyl acrylate), poly(butylacrylate), poly(acrylonitrile), a copolymer of ethylhexyl acrylate and methyl methacrylate, a copolymer of butylacrylate 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 thereof. A membrane characterized by:

7. In paragraph 1, A separator characterized in that the peel strength between the porous polymer substrate and the porous coating layer is 50 gf / 15 mm or more.

8. In paragraph 1, A separator characterized in that the adhesive layer does not contain inorganic particles.

9. Including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, An electrochemical device characterized in that the above separator is a separator according to any one of claims 1 to 8.

10. Step of preparing a porous polymer substrate; A step of preparing a slurry for forming an adhesive layer including a first binder polymer and a first aqueous solvent, and applying and drying the slurry for forming an adhesive layer on at least one surface of the porous polymer substrate to form an adhesive layer; A step of preparing a slurry for forming a heat-resistant layer including inorganic particles, a second binder polymer, a second aqueous solvent, and an organic solvent, and applying and drying the slurry for forming a heat-resistant layer on one surface of the adhesive layer to form a heat-resistant layer; The above first binder polymer comprises an acrylic polymer, A method for manufacturing a separation membrane, characterized in that the swelling ratio of the acrylic polymer is 50% or more.

11. In paragraph 10, A method for manufacturing a separation membrane, characterized in that the organic solvent comprises a carbonate system.

12. In paragraph 10, A method for manufacturing a membrane, characterized in that the organic solvent comprises dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and ethylmethyl carbonate or a mixture thereof.

13. In paragraph 10, A method for manufacturing a separation membrane, characterized in that the second aqueous solvent and the organic solvent are mixed in a volume ratio of 95:5 to 80:20.