Separator and electrochemical device comprising the same

Abstract

Disclosed is a separator including: a porous polymer substrate; and a porous coating layer provided on at least one surface of the porous polymer substrate and including a plurality of inorganic particles and an adhesive polymer partially or entirely provided on surfaces of the inorganic particles to allow the inorganic particles to be interconnected and fixed, wherein the adhesive polymer includes core-shell type polymer particles having a core portion and a shell portion surrounding the core portion, a core portion polymer contained in the core portion and a shell portion polymer contained in the shell portion have different glass transition temperatures, and a polymer containing a component capable of being eluted with an electrolyte and being connected by a chemical bond is grafted to a surface of the shell portion. Also disclosed is an electrochemical device including the separator.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a separator and an electrochemical device including the same. Specifically, the present disclosure relates to a separator that exhibits improved adhesion to an electrode in an electrolyte, and an electrochemical device including the same.

[0002] This application claims priority to Korean Patent Application No. 10-2020-0136313, filed on October 20, 2020, in Korea, the disclosure of which is incorporated herein by reference. BACKGROUND

[0003] Recently, energy storage technology has received growing interest. As the application of energy storage technology has expanded to energy for mobile phones, camcorders, and notebook computers, and even to energy for electric vehicles, efforts to develop electrochemical devices have increasingly become a reality. In this context, electrochemical devices have received the most attention. Among these electrochemical devices, the development of rechargeable secondary batteries has been of great interest. Recently, in the process of developing these batteries, in order to improve the capacity density and specific energy, active research has been conducted on designing new electrodes and batteries.

[0004] Among the commercially available secondary batteries, lithium secondary batteries developed in the early 1990s have received much attention because they have a higher operating voltage and a significantly higher energy density compared to conventional batteries such as Ni-MH batteries, Ni-Cd batteries, and sulfuric acid-lead batteries using aqueous electrolytes. However, such lithium ion batteries cause safety-related problems such as fire and explosion due to the use of organic electrolytes, and have the disadvantage of being difficult to manufacture.

[0005] Recently, lithium ion polymer batteries have improved these disadvantages of lithium ion batteries and are expected to be one of the next-generation batteries. However, such lithium ion polymer batteries still provide a relatively low capacity compared to lithium ion batteries, and in particular, exhibit an insufficient discharge capacity at low temperatures. Therefore, there is an urgent need to improve such disadvantages.

[0006] Although these electrochemical devices have been produced by many manufacturing companies, their safety characteristics show different signs. It is very important to evaluate and ensure the safety of these electrochemical devices. The most important consideration is that electrochemical devices should not cause injury to users when they malfunction. For this purpose, safety standards strictly control the ignition and smoke emission in electrochemical devices. Of particular concern for the safety characteristics of electrochemical devices is the occurrence of explosion when the electrochemical device overheats to thermal runaway or the perforation of the separator. In particular, polyolefin-based porous substrates conventionally used as separators for electrochemical devices exhibit serious thermal shrinkage behavior at a temperature of 100°C or higher due to their material properties and characteristics during the manufacturing process, including orientation, thereby causing short-circuiting between the cathode and the anode.

[0007] To solve the safety problems of the above-mentioned electrochemical devices, a separator having a porous organic-inorganic coating formed by applying an excess of a mixture of inorganic particles and a binder polymer to at least one surface of a porous substrate having a plurality of pores has been proposed.

[0008] The binder polymer for the porous organic-inorganic coating can be classified into an organic binder and an aqueous binder depending on the type of the dispersion medium of the composition used to form the coating. According to the prior art, an organic dispersion medium and an organic binder have been frequently used. However, as environmental problems have recently become a particular issue, an aqueous dispersion medium and an aqueous binder have received increasing attention.

[0009] Here, one of the technical problems of the aqueous binder compared to the organic binder is to ensure wet adhesion and long-term adhesion.

[0010] In the case of the organic binder, adhesion gradually increases as the binder molecules penetrate into the substrate over time after adhesion. Therefore, adhesion can be easily maintained even when the electrode swells / shrinks in a state of being wetted by the electrolyte during cycling.

[0011] On the contrary, in the case of the aqueous binder, since the aqueous binder does not dissolve in the electrolyte and does not show an entanglement effect, adhesion is essentially not increased over time. Therefore, such an aqueous binder is more likely to cause interfacial separation due to a lack of adhesion in a state of being wetted by the electrolyte and in the case of electrode swelling / shrinking during cycling, thereby causing degradation of the life characteristics of the battery.

[0012] To overcome the above problems, it has been suggested to add an additive having an entanglement effect to the composition for forming the porous coating. However, in this case, the additive can cause side effects such as clogging the pores of the porous polymer substrate. SUMMARY

[0013] Technical Problem

[0014] The present disclosure aims to solve the problems of the prior art, and thus aims to provide a separator that exhibits improved adhesion to an electrode in an electrolyte.

[0015] The present disclosure also aims to provide an electrochemical device including the separator.

[0016] Technical Solution

[0017] In one aspect of the present disclosure, a separator according to any one of the following embodiments is provided.

[0018] According to a first embodiment, a separator is provided, comprising:

[0019] a porous polymer substrate; and

[0020] a porous coating layer disposed on at least one surface of the porous polymer substrate and including a plurality of inorganic particles and an adhesive polymer partially or entirely disposed on surfaces of the inorganic particles to allow the inorganic particles to be interconnected and fixed,

[0021] wherein the adhesive polymer includes core-shell type polymer particles having a core portion and a shell portion surrounding the core portion,

[0022] a core portion polymer contained in the core portion and a shell portion polymer contained in the shell portion have different glass transition temperatures, and

[0023] a polymer containing a component capable of being eluted with an electrolyte and being connected by a chemical bond is grafted to the surface of the shell portion.

[0024] According to a second embodiment, the separator as defined in the first embodiment is provided, wherein the glass transition temperature of the core portion polymer is higher than the glass transition temperature of the shell portion polymer.

[0025] According to a third embodiment, the separator as defined in the second embodiment is provided, wherein the glass transition temperature of the core portion polymer is 85°C or more, and the glass transition temperature of the shell portion polymer is -100°C to 20°C.

[0026] According to a fourth embodiment, there is provided the separator as defined in the second embodiment or the third embodiment, wherein the core portion polymer includes polystyrene, a polystyrene copolymer, polymethyl methacrylate, a polymethyl methacrylate copolymer, a polyamide-based polymer, or two or more thereof, and the shell portion polymer includes an acrylate-based polymer, a rubber-based polymer, a urethane-based polymer, a silicone-based polymer, or two or more thereof.

[0027] According to a fifth embodiment, there is provided the separator as defined in the first embodiment, wherein a glass transition temperature of the core portion polymer is lower than a glass transition temperature of the shell portion polymer.

[0028] According to a sixth embodiment, there is provided the separator as defined in the fifth embodiment, wherein the glass transition temperature of the core portion polymer is -100°C to 20°C, and the glass transition temperature of the shell portion polymer is 85°C or higher.

[0029] According to a seventh embodiment, there is provided the separator as defined in the fifth embodiment or the sixth embodiment, wherein the core portion polymer includes an acrylate-based polymer, a rubber-based polymer, a urethane-based polymer, a silicone-based polymer, or two or more thereof, and the shell portion polymer includes a polystyrene-based polymer, a poly(meth)acrylate-based polymer, a polyamide-based polymer, or two or more thereof.

[0030] According to an eighth embodiment, there is provided the separator as defined in any one of the first embodiment to the seventh embodiment, wherein an average particle diameter of the core-shell type polymer particle is 100 nm to 1 μm.

[0031] According to a ninth embodiment, there is provided the separator as defined in any one of the first embodiment to the eighth embodiment, wherein a ratio of an average particle diameter of the core portion based on an average particle diameter of the core-shell type polymer particle is 50% - 90%.

[0032] According to a tenth embodiment, there is provided the separator as defined in any one of the first embodiment to the ninth embodiment, wherein the core-shell type polymer particle includes 100 parts by weight of the core portion and 100 - 300 parts by weight of the shell portion.

[0033] According to an eleventh embodiment, there is provided the separator as defined in any one of the first embodiment to the tenth embodiment, wherein the polymer grafted to the surface of the shell portion includes polyvinyl alcohol (PVA) or a copolymer thereof, polyethylene glycol (PEG) or a copolymer thereof, polypropylene glycol (PPG) or a copolymer thereof, polyvinyl acetate (PVAc) or a copolymer thereof, polyacrylonitrile (PAN) or a copolymer thereof, or two or more thereof.

[0034] According to a twelfth embodiment, there is provided the separator as defined in any one of the first to eleventh embodiments, wherein the content of the polymer grafted to the surface of the shell portion is 1 to 30% by weight, based on the total weight of the core-shell polymer particles.

[0035] According to a thirteenth embodiment, there is provided the separator as defined in any one of the first to twelfth embodiments, wherein the core-shell polymer particles include: core-shell polymer particles in which the shell portion polymer has a higher glass transition temperature than the core portion polymer; core-shell polymer particles in which the shell portion polymer has a lower glass transition temperature than the core portion polymer; or both.

[0036] According to a fourteenth embodiment, there is provided the separator as defined in any one of the first to thirteenth embodiments, wherein the porous polymer substrate is a polyolefin-based porous polymer substrate.

[0037] According to a fifteenth embodiment, there is provided an electrochemical device including a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the same as defined in any one of the first to fourteenth embodiments.

[0038] According to a sixteenth embodiment, there is provided the electrochemical device as defined in the fifteenth embodiment, which is a lithium secondary battery.

[0039] Beneficial Effects

[0040] According to embodiments of the present disclosure, the binder polymer used in the porous coating layer of the separator includes core-shell polymer particles having a core portion and a shell portion surrounding the core portion, and a polymer containing a component capable of being eluted with an electrolyte and connected by a chemical bond is grafted to the surface of the shell portion. In this way, the wet adhesion and interface retention between the separator and the electrode in the electrolyte are improved by the entanglement phenomenon between the grafted chain and the electrolyte, thereby improving the long-term life characteristics of the electrochemical device using the separator.

[0041] Further, the core portion polymer contained in the core portion of the core-shell type polymer particle and the shell portion polymer contained in the shell portion thereof are controlled to have different glass transition temperatures. Specifically, when a soft polymer having a lower glass transition temperature is used in the shell portion and a hard polymer having a higher glass transition temperature is used in the core portion, the disadvantage of the aqueous binder, i.e., the ability of the electrolyte to penetrate into the interface with the binder polymer is reduced, and thus in a state of being wetted with the electrolyte, the adhesion between the separator and the electrode can be significantly improved. Further, when a hard polymer having a higher glass transition temperature is used in the shell portion and a soft polymer having a lower glass transition temperature is used in the core portion, excessive swelling due to impregnation of the soft polymer of the core portion with the electrolyte can be suppressed, and thus the reduction or clogging of the pores of the porous coating layer caused by swelling of the core-shell type polymer particle can be prevented, and thus the gas permeability can be ensured and the problem of increased resistance can be solved. DETAILED DESCRIPTION

[0042] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it is to be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings and should be interpreted based on the meanings and concepts corresponding to the technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation of the invention.

[0043] In one aspect of the present disclosure, a separator is provided, including:

[0044] a porous polymer substrate; and

[0045] a porous coating layer disposed on at least one surface of the porous polymer substrate and including a plurality of inorganic particles and a binder polymer partially or entirely disposed on the surfaces of the inorganic particles so that the inorganic particles can be connected and fixed to each other,

[0046] wherein the binder polymer includes core-shell type polymer particles having a core portion and a shell portion surrounding the core portion,

[0047] a core portion polymer contained in the core portion and a shell portion polymer contained in the shell portion have different glass transition temperatures, and

[0048] a polymer containing a component capable of being eluted with an electrolyte and being connected by a chemical bond is grafted to the surface of the shell portion.

[0049] According to embodiments of the present disclosure, the glass transition temperature of the core portion polymer can be higher than the glass transition temperature of the shell portion polymer.

[0050] Here, the core portion polymer can have a glass transition temperature of 85°C or more, 85°C to 150°C, or 85°C to 100°C. The shell portion polymer can have a glass transition temperature of -100°C to 20°C, -70°C to 20°C, or -40°C to 20°C.

[0051] Specific examples of the core portion polymer include a polystyrene-based polymer, a poly(meth)acrylate-based polymer, a polyamide-based polymer, or two or more of them. Specific examples of the shell portion polymer include an acrylate-based polymer, a rubber-based polymer, a urethane-based polymer, a silicone-based polymer, or two or more of them.

[0052] More specifically, the poly(meth)acrylate-based polymer can include a homopolymer or copolymer of poly(meth)acrylate, a homopolymer or copolymer of poly(alkyl(meth)acrylate), poly(alkyl acrylate)-co-(alkyl(meth)acrylate), a homopolymer or copolymer of poly(fluoroalkyl(meth)acrylate), polyacrylonitrile, a homopolymer or copolymer of polyester, or two or more of them. For example, the alkyl group can be a C1-C30 alkyl group, a C1-C15 alkyl group, a C1-C10 alkyl group, or a C1-C5 alkyl group.

[0053] For example, a polymer such as a polystyrene molecule exists in a solid state at room temperature, and thus such a polymer is glassy and weak at room temperature. When a polystyrene polymer is observed, while the temperature is increased, the molecular backbone frozen at a certain temperature starts Brownian motion (intramolecular motion caused by rotation of intramolecular bonds; the entire molecule does not move significantly to change its position), and thus the specific volume rapidly increases and the polymer undergoes a transition to a rubber phase. This phase change, i.e., a change from a glass phase to a rubber phase, is called a glass transition, and the temperature at which this phase change occurs is called a glass transition temperature, T g (T represents temperature, and g is the initial letter of glass). Since a polymer material becomes hard, weak, or soft around this temperature, T g is considered to be one of important physical properties of a polymer. In addition, since a polymer material undergoes changes in mechanical strength, size, etc. at the temperature at which Brownian motion begins, i.e., T g , it is necessary to pay attention to the use conditions of a resin and T g depending on the type of polymer. The difference in T g is caused by a difference in the structure or composition of the polymer.

[0054] According to embodiments of this disclosure, the glass transition temperature can be determined using a differential scanning calorimeter (DSC) or the like. Specific examples of DSC instruments include DSC (DSC823, METTLER TOLEDO), DSC (TAInstrument), or the like.

[0055] In core-shell polymer particles having a core portion and a shell portion surrounding the core portion, when the T of the core portion... g T above the shell g At that time, even when the T of the shell portion on the surface portion of the core-shell polymer particle is reduced in order to improve the adhesion between the separator and the electrode, g At that time, due to the high T of the core part g The particles retain their shape, so the separator does not cause an increase in resistance. Therefore, the increase in resistance can be minimized and adhesion to the electrode can be enhanced.

[0056] According to embodiments of this disclosure, the T-section between the core portion and the shell portion of the core-shell polymer particle... g The temperature difference can be 10℃-200℃, 15℃-180℃, 20℃-160℃, or 20℃-80℃.

[0057] The ratio of the average particle size of the core portion to the average particle size of the core-shell polymer particles can be 50-90%, 60-90%, 70-90%, 80-90%, or 80-85%. When the ratio of the average particle size of the core portion to the average particle size of the core-shell polymer particles meets the above ranges, the core portion retains its shape and the shell portion exhibits improved adhesion, thereby improving the performance of the separator.

[0058] According to this disclosure, the average particle size of core-shell polymer particles, the average particle size of inorganic particles, and the average particle size of the core portion can be determined using a particle size analyzer (laser particle size analyzer, purchased from Malvern). For example, the average particle size of the core portion can be determined after the core portion is prepared, and the average particle size of the entire particle can be determined after the shell portion is prepared.

[0059] Core-shell polymer particles may comprise 100 parts by weight of a core portion and 10-300 parts by weight, 10-250 parts by weight, 80-250 parts by weight, 120-250 parts by weight, 200-250 parts by weight, or 80-120 parts by weight of a shell portion. When the weight ratio of the core portion to the shell portion meets the above ranges, improved wet adhesion properties can be provided while controlling the increase in battery resistance by improving air permeability.

[0060] According to embodiments of the present disclosure, the glass transition temperature of the core portion polymer can be lower than the glass transition temperature of the shell portion polymer. In other words, the shell portion polymer can have a higher glass transition temperature than the core portion polymer.

[0061] Here, the shell portion polymer can have a glass transition temperature of 85°C or more, 85°C to 150°C, or 85°C to 100°C. The core portion polymer can have a glass transition temperature of -100°C to 20°C, -70°C to 20°C, or -40°C to 20°C.

[0062] Specific examples of the shell portion polymer include a polystyrene-based polymer, a poly(meth)acrylate-based polymer, a polyamide-based polymer, or two or more thereof.

[0063] Specific examples of the core portion polymer include an acrylate-based polymer, a rubber-based polymer, a urethane-based polymer, a silicone-based polymer, or two or more thereof.

[0064] More specifically, the poly(meth)acrylate-based polymer can include a homopolymer or copolymer of poly(meth)acrylate, a homopolymer or copolymer of poly(alkyl(meth)acrylate), poly(alkyl acrylate)-co-(alkyl(meth)acrylate), a homopolymer or copolymer of poly(fluoroalkyl(meth)acrylate), polyacrylonitrile, a homopolymer or copolymer of a polyester, or two or more thereof. For example, the alkyl group can be a C1-C30 alkyl group, a C1-C15 alkyl group, a C1-C10 alkyl group, or a C1-C5 alkyl group.

[0065] The average particle diameter ratio of the core portion based on the average particle diameter of the core-shell polymer particle can be 50-90%, 60-90%, 70-90%, 80-90%, or 80-85%. When the average particle diameter ratio of the core portion based on the average particle diameter of the core-shell polymer particle satisfies the above range, the core portion is inhibited from swelling through the shell portion while the adhesion of the core portion is maintained, thereby improving the performance of the separator.

[0066] In the core-shell polymer particle according to the present disclosure, a polymer containing a component capable of being eluted with an electrolyte and being connected by a chemical bond is grafted to the surface of the shell portion.

[0067] Here, the "polymer containing a component capable of being eluted with an electrolyte" refers to a polymer having a chemical structure having affinity with an electrolyte at at least one position selected from the main chain and the side chain of the polymer, so that no phase separation occurs between the polymer and the electrolyte when mixed with the electrolyte.

[0068] According to embodiments of the present disclosure, the grafting polymer can include polyvinyl alcohol (PVA) or a copolymer thereof, polyethylene glycol (PEG) or a copolymer thereof, polypropylene glycol (PPG) or a copolymer thereof, polyvinyl acetate (PVAc) or a copolymer thereof, polyacrylonitrile (PAN) or a copolymer thereof, or two or more of them.

[0069] The content of the grafting polymer can be 1-30 wt%, 1-25 wt%, or 1-20 wt% based on the total weight of the core-shell polymer particles. When the content of the grafting polymer satisfies the above range, adhesion between the separator and the electrode can be improved by entanglement with the electrolyte, interface retention between the separator and the electrode can be improved, long-term life characteristics of the electrochemical device using the separator can be improved, and battery stability can be facilitated.

[0070] According to embodiments of the present disclosure, a method for grafting a polymer containing a component capable of being eluted with an electrolyte to the surface of the shell portion can include the following steps: (1) mixing core-shell polymer particles dispersed in a solvent with a polymer capable of being eluted with an electrolyte (e.g., a polymer having high crosslinking activity by coupling agent treatment) dispersed in a solvent; (2) performing sonification treatment; (3) removing unreacted substances by centrifugal separation; and (4) vacuum drying the remaining product.

[0071] The core-shell polymer particles can have an average particle diameter of 100 nm to 1 µm, 300 nm to 1 µm, or 300-800 nm. When the average particle diameter of the core-shell polymer particles satisfies the above range, when the porous coating further includes inorganic particles, the porous coating can be formed into a thin film and uniformly mixed with the inorganic particles.

[0072] According to embodiments of the present disclosure, the core-shell polymer particles can include: core-shell polymer particles in which the shell portion polymer has a higher glass transition temperature than the core portion polymer; core-shell polymer particles in which the shell portion polymer has a lower glass transition temperature than the core portion polymer; or both of the core-shell polymer particles.

[0073] Specifically, the core-shell type polymer particles can include only core-shell type polymer particles in which the core portion polymer has a higher glass transition temperature than the shell portion polymer; only core-shell type polymer particles in which the core portion polymer has a lower glass transition temperature than the shell portion polymer; or a combination of core-shell type polymer particles in which the core portion polymer has a higher glass transition temperature than the shell portion polymer and core-shell type polymer particles in which the core portion polymer has a lower glass transition temperature than the shell portion polymer. When a combination of two types of particles is used, the weight ratio of the particles in which the core portion polymer has a higher glass transition temperature than the shell portion polymer to the particles in which the core portion polymer has a lower glass transition temperature than the shell portion polymer can be 9:1 to 1:9, 7:3 to 3:7, 7:3 to 5:5, or 5:5 to 7:3.

[0074] According to the present disclosure, the average particle diameter (D50) of the inorganic particles and the core-shell type polymer particles described below can be defined as the particle diameter at the 50% point in the particle diameter distribution. For example, the average particle diameter (D50) of the core-shell type polymer particles and the inorganic particles can be determined by using an electron microscope such as a scanning electron microscope (SEM) or a field emission scanning electron microscope (FE-SEM), or by using a laser diffraction method. Specifically, in the case of the laser diffraction method, the average particle diameter (D50) can be determined by the following method: dispersing the core-shell type polymer particles or the inorganic particles in a dispersion medium, introducing the resulting product into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT3000), irradiating it with ultrasonic waves having a frequency of about 28 kHz at an output of 60 W, and calculating the average particle diameter (D50) at the 50% point in the particle diameter distribution determined by the analyzer.

[0075] Specifically, the porous polymer substrate can be a porous polymer film substrate or a porous polymer nonwoven fabric substrate.

[0076] The porous polymer film substrate can be a porous polymer film including a polyolefin such as polyethylene or polypropylene. Such a polyolefin porous polymer film substrate achieves a closing function at a temperature of 80 to 130°C.

[0077] Here, the polyolefin porous polymer film substrate can be formed of a polymer including a polyolefin polymer such as polyethylene (including high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene), polypropylene, polybutene, or polyamylene, alone or in combination of two or more thereof.

[0078] Further, the porous polymer film substrate can be obtained by molding various polymers such as a polyester other than a polyolefin into a film shape. Further, the porous polymer film substrate can have a stacked structure of two or more film layers, each of which can be formed of a polymer including the above-described polymer such as a polyolefin or a polyester, alone or in combination of two or more thereof.

[0079] Further, the porous polymer film substrate and the porous polymer nonwoven fabric substrate can be formed of polyethyleneterephthalate, polybutyleneterephthalate, a polyester, a polyacetal, a polyamide, a polycarbonate, a polyimide, a polyetheretherketone, a polyethersulfone, a polyphenyleneoxide, a polyphenylenesulfide, a polyethylenenaphthalene, alone or in combination, in addition to the above-described polyolefin.

[0080] The thickness of the porous polymer substrate is not particularly limited, and the thickness of the porous polymer substrate is 1-100 μm, specifically 5-50 μm. Although the size of the pores and the porosity present in the porous polymer substrate are not particularly limited, the pore diameter and the porosity can be 0.01-50 μm and 10%-95%, respectively.

[0081] Specific examples of the inorganic particles included in the porous coating layer can include high-dielectric-constant inorganic particles having a dielectric constant of 5 or more, specifically 10 or more, inorganic particles capable of transporting lithium ions, or a mixture thereof.

[0082] Non-limiting examples of the inorganic particles having a dielectric constant of 5 or more can include BaTiO3, Pb(Zr,Ti)O3(PZT), Pb(Mg 1-x La x Zr 1-y Ti y O3(PLZT), Pb(Mg 1 / 3 Nb2 / 3 ) O3-PbTiO3 (PMN-PT), hafnium dioxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, SiO2, Y2O3, Al2O3, TiO2, SiC, AlO(OH), Al2O3.H2O, or a mixture thereof.

[0083] As used herein, the term "inorganic particles capable of transporting lithium ions" refers to inorganic particles that contain lithium element and do not store lithium but transport lithium ions. Non-limiting examples of inorganic particles capable of transporting lithium ions include lithium phosphate (Li3PO4), lithium titanium phosphate (LixTiy(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 (LiAlTiP) x Oy-based glass (1 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), such as Li 3.25 Ge 0.25 P 0.75 S4 of lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), such as lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), such as SiS2-based glass (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4), and such as P2S5-based glass (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7), or a mixture thereof.

[0084] Further, the average particle diameter ratio of the core-shell polymer particles based on the average particle diameter of the inorganic particles can be 80% to 200%, specifically 80% to 190% / or 84% to 188%. When the average particle diameter ratio of the core-shell polymer particles based on the average particle diameter of the inorganic particles is 80% to 200%, the core-shell polymer particles can be distributed on the surface of the separator, so that the separator can be advantageously adhered to the electrode.

[0085] Although the thickness of the porous coating layer is not particularly limited, the thickness can be 1 to 10 μm, or 1.5 to 6 μm. Further, the porosity of the porous coating layer is not particularly limited, but is preferably 35% to 65%.

[0086] The weight ratio of the core-shell polymer particles to the inorganic particles can be 5:95 to 80:20, 20:80 to 80:20, or 50:50 to 80:20. When the weight ratio satisfies the range defined above, the stability of the battery can be improved by the core-shell polymer particles, while the heat resistance of the porous coating layer is secured.

[0087] The separator according to the embodiments of the present disclosure can further include other additives as a component of the porous coating layer.

[0088] According to the embodiments of the present disclosure, the porous coating layer can be an aqueous coating layer using an aqueous slurry. In the case of the aqueous coating layer, thin film coating is facilitated and the electrical resistance of the separator is advantageously reduced.

[0089] Hereinafter, a method for manufacturing a separator according to the embodiments of the present disclosure will be explained.

[0090] To form the porous coating layer, the inorganic particles and the core-shell polymer particles are added and dispersed in an aqueous dispersion medium to prepare a composition for forming the porous coating layer. The inorganic particles can be added after being previously pulverized to a predetermined average particle diameter. Alternatively, the inorganic particles can be added to a binder polymer solution, and then pulverized and dispersed while being controlled to have a predetermined diameter by using a ball milling process or the like.

[0091] The core-shell polymer particles can be prepared by various known methods, such as emulsion polymerization, suspension polymerization, massive polymerization, solution polymerization, bulk polymerization, or the like. For example, the core-shell polymer particles can be prepared by emulsion polymerization.

[0092] Although the method of coating the composition for forming a porous coating layer on the porous polymer substrate is not particularly limited, it is preferable to use a slit coating process or a dip coating process. The slit coating process includes coating the composition supplied through a slit die onto the entire surface of the substrate, and is capable of controlling the thickness of the coating layer according to the flux supplied from the metering pump. Further, the dip coating process includes immersing the substrate in a tank containing the composition to perform coating, and is capable of controlling the thickness of the coating layer according to the concentration of the composition and the rate at which the substrate is removed from the tank. Further, in order to more precisely control the coating thickness, post-metering can be performed by a Mayer bar or the like after immersion.

[0093] Then, the porous polymer substrate coated with the composition for forming a porous coating layer can be dried in a dryer such as an oven to form a porous coating layer on at least one surface of the porous polymer substrate.

[0094] After the composition for forming a porous coating layer is coated on the porous polymer substrate, the dispersed medium can be removed by drying the composition at 90-180°C, specifically 100-150°C.

[0095] According to the embodiments of the present disclosure, the core-shell type polymer particles of the porous coating layer attach the inorganic particles to each other such that they can maintain their combined state (i.e., the core-shell type polymer particles interconnect and fix the inorganic particles), and the inorganic particles can be combined to the porous polymer substrate through the core-shell type polymer particles. The inorganic particles and the core-shell type polymer particles of the porous coating layer can form an interstitial volume while being substantially in contact with each other. Here, the interstitial volume refers to a space defined by the inorganic particles and the core-shell type particles which are substantially in contact with each other in a closely packed or densely packed structure of the inorganic particles and the core-shell type particles. The interstitial volume between the inorganic particles and the core-shell type polymer particles becomes an empty space to form pores of the porous coating layer. Here, the polymer contained in the shell portion of the core-shell type polymer particles functions as an adhesive during the drying process such that the shell portions of the core-shell type polymer particles can be interconnected and fixed, and the porous polymer substrate can be interconnected with the core-shell type polymer particles. In this way, the porous coating layer can be formed.

[0096] Non-limiting examples of the dispersion medium used herein include water alone, or a mixture of water and any one compound selected from the group consisting of methanol, ethanol, isopropanol, and isopropanol.

[0097] In another aspect of the present disclosure, an electrochemical device is provided, including a cathode, an anode, and a separator interposed between the cathode and the anode, wherein the separator is the separator according to the embodiments of the present disclosure described above.

[0098] The electrochemical device includes any device that performs an electrochemical reaction, and specific examples thereof include primary batteries, secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor devices of all types. Specifically, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries are preferred.

[0099] The two electrodes, i.e., the cathode and the anode, used in combination with the separator according to the present disclosure are not particularly limited, and can be obtained by combining an electrode active material with an electrode current collector using a conventional method known in the art. Among the electrode active materials, non-limiting examples of the cathode active material include conventional cathode active materials that can be used in a cathode of a conventional electrochemical device. Specifically, it is preferred to use lithium manganese oxides, lithium cobalt oxides, lithium nickel oxides, lithium iron oxides, or lithium composite oxides containing combinations thereof. Non-limiting examples of the anode active material include conventional anode active materials that can be used in an anode of a conventional electrochemical device. Specifically, it is preferred to use lithium intercalation materials such as lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials. Non-limiting examples of the cathode current collector include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of the anode current collector include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0100] The electrolyte that can be used in the electrochemical device according to the present disclosure is a salt having the structure of A + B - wherein A + includes an alkali metal cation such as Li + , Na + , K + , or combinations thereof, and B - includes an anion such as PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 -Anions, or combinations thereof, of which the salt is dissolved or dissociated in organic solvents including 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), γ-butyrolactone, or combinations thereof. However, this disclosure is not limited thereto.

[0101] Depending on the manufacturing process of the final product and the required properties of the final product, electrolyte injection can be performed at appropriate steps during the battery manufacturing process. In other words, electrolyte injection can be performed before battery assembly or in the final step of battery assembly.

[0102] The embodiments will be described more fully below to facilitate a clear understanding of this disclosure. However, the following embodiments may be embodied in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided to make this disclosure thorough and complete, and to fully convey the scope of this disclosure to those skilled in the art.

[0103] Example 1

[0104] First, alumina (Al₂O₃) with an average particle size (D50) of 500 nm and core-shell polymer particles (CSG₁) containing components that can be eluted with electrolytes and are chemically bonded were grafted onto the surface of the shell portion in water at a weight ratio of 8:2. The resulting mixture was then dispersed with the beads for 2 hours using a paint shaker to prepare a slurry for porous coatings. Here, the core portion of the core-shell polymer particles comprises polystyrene (T… g :100℃), the shell part includes polyurethane (T g The temperature is -30℃), and the grafted polymer is polyvinyl alcohol. Based on the total weight of the core-shell polymer particles, the grafted polymer content is 10% by weight. The average particle size (D50) of the core-shell polymer particles is 300 nm. The ratio of the average particle size of the core portion to the average particle size of the core-shell polymer particles is 80%.

[0105] The obtained slurry was coated onto both surfaces of a polyethylene porous membrane (thickness: 12 μm) by dip coating process and dried at 85 °C for 2 hours to obtain a separator with a porous coating (thickness: 1.5 μm) on each of its two surfaces (total thickness: 15 μm).

[0106] Example 2

[0107] First, alumina (AI2O3) having an average particle diameter (D50) of 500 nm and core-shell type polymer particles (CSG2) in which a polymer containing a component capable of being eluted with an electrolyte and being connected by a chemical bond is grafted to the surface of the shell portion were mixed with each other in water at a weight ratio of 8:2, and the resulting mixture was dispersed with beads for 2 hours by using a paint shaker to prepare a slurry for a porous coating. Here, the core portion of the core-shell type polymer particles includes polyurethane (T g : -30°C), the shell portion includes polystyrene (T g : 100°C), and the grafted polymer is polyvinyl alcohol. The content of the grafted polymer was 10% by weight based on the total weight of the core-shell type polymer particles. The average particle diameter (D50) of the core-shell type polymer particles was 300 nm. The ratio of the average particle diameter of the core portion based on the average particle diameter of the core-shell type polymer particles was 80%.

[0108] The resulting slurry was coated on both surfaces of a polyethylene porous film (thickness: 12 μm) by a dip coating process, and dried at a temperature of 85°C for 2 hours to obtain a separator (total thickness: 15 μm) having a porous coating (thickness: 1.5 μm) on each of both surfaces thereof.

[0109] Example 3

[0110] First, alumina (AI2O3) having an average particle diameter (D50) of 500 nm, core-shell type polymer particles (CSG1) including a polymer grafted to the surface of the shell portion according to Example 1, and core-shell type polymer particles (CSG2) including a polymer grafted to the surface of the shell portion according to Example 2 were mixed with each other in water at a weight ratio of 8:2:1, and the resulting mixture was dispersed with beads for 2 hours by using a paint shaker to prepare a slurry for a porous coating.

[0111] The resulting slurry was coated on both surfaces of a polyethylene porous film (thickness: 12 μm) by a dip coating process, and dried at a temperature of 85°C for 2 hours to obtain a separator (total thickness: 15 μm) having a porous coating (thickness: 1.5 μm) on each of both surfaces thereof.

[0112] Comparative Example 1

[0113] A separator was obtained in the same manner as in Example 1, except that alumina (AI2O3) having an average particle diameter (D50) of 500 nm and polyurethane (T g: 100°C) was mixed in water at a weight ratio of 8:2, and the resulting mixture was dispersed with the beads for 2 hours by using a paint shaker to prepare a slurry for a porous coating.

[0114] Comparative Example 2

[0115] A separator was obtained in the same manner as in Example 1, except that a slurry for a porous coating was prepared by using core-shell type polymer particles in which a polymer containing a component capable of being eluted with an electrolyte and connected by a chemical bond was not grafted to the surface of the shell portion.

[0116] Here, the core portion of the core-shell type polymer particles includes polystyrene (T g : 100°C), and the shell portion includes polyurethane (T g : -30°C).

[0117] Comparative Example 3

[0118] A separator was obtained in the same manner as in Example 2, except that a slurry for a porous coating was prepared by using core-shell type polymer particles in which a polymer containing a component capable of being eluted with an electrolyte and connected by a chemical bond was not grafted to the surface of the shell portion.

[0119] Here, the core portion of the core-shell type polymer particles includes polyurethane (T g : -30°C), and the shell portion includes polystyrene (T g : 100°C).

[0120] Test Method and Results

[0121] Method of Measuring Glass Transition Temperature

[0122] The glass transition temperature (T g ) of each core portion and each shell portion of the core-shell type polymer particles used according to Examples 1-3 and Comparative Examples 1-3 was measured by using a differential scanning calorimeter (DSC) (DSC823, METTLER TOLEDO).

[0123] Average Particle Diameter (D50)

[0124] The average particle diameter (D50) was determined by dispersing the core-shell type polymer particles or inorganic particles used according to Examples 1-3 and Comparative Examples 1-3 in a dispersion medium, introducing the resulting product into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasonic waves at a frequency of about 28 kHz at an output of 60 W, and calculating the average particle diameter (D50) at the 50% point in the particle diameter distribution determined by the analyzer. The average particle diameter of the core portion of each type of core-shell type polymer particle was calculated in the same manner as described above by using the core portion particles before the shell portion was formed.

[0125] Air Permeability (Gurley)

[0126] The gas permeability of the separators according to each of Examples 1-3 and Comparative Examples 1-3 was determined by using the method of ASTM D726-94. The results are shown in Table 1 below. Here, "Gurley" refers to the resistance to air flow and is measured by using a Gurley densometer. The gas permeability values described herein are expressed as time (sec), i.e., 100 cc of air passing through the separator of each of Examples 1-3 and Comparative Examples 1-3 at a pressure of 12.2 in H2O. 2 Time (sec) required for the cross section, i.e., air permeation time.

[0127] Resistance (ER)

[0128] The separators according to each of Examples 1-3 and Comparative Examples 1-3 were impregnated with an electrolyte (ethylene carbonate (EC): diethyl carbonate (DEC) = 3:7, LiPF61.0M) and the AC resistance was measured. The results are shown in Table 1 below. Here, "AC resistance" is the resistance value measured at 1 kHz using an instrument purchased from Hioki.

[0129] Adhesion to the Cathode under Electrolyte Wetting

[0130] - Test instrument: UTM (LLOYD INSTRUMENT LS 1)

[0131] - Preparation and test method of sample

[0132] First, a cobalt lithium-based composite oxide, a conductive material (Denka black), and a binder (PVdF) were weighed in a weight ratio of 95:2.5:2.5, these ingredients were introduced into N-methyl pyrrolidone (NMP) and mixed to prepare a cathode mixture. The cathode mixture was coated on an aluminum foil having a thickness of 20 to 200 μm, followed by pressure application and drying to obtain a cathode.

[0133] The electrolyte used herein was prepared by dissolving 1M LiPF6 in a mixed solvent containing ethyl carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1:1.

[0134] Next, 1) the cathode and the separator were cut to a size of 20 x 60 mm. 2) The cathode was stacked with the separator, the resulting structure was inserted into an aluminum (Al) pouch, the aluminum pouch was cut to a size of 200 x 80 mm and folded to a size of 100 x 80 mm, and then side-sealed. 3) The electrolyte was injected into the pouch in an amount of 1 g, and then vacuum-sealed. 4) The sealed pouch cell was pre-aged for 1 day. 5) The pre-aged pouch cell was heated / pressurized at 5 kgf / cm2for 10 minutes by a jig configured to fix the pre-aged pouch cell. 2 Next, 1) the cathode and the separator were cut to a size of 20 x 60 mm. 2) The cathode was stacked with the separator, the resulting structure was inserted into an aluminum (Al) pouch, the aluminum pouch was cut to a size of 200 x 80 mm and folded to a size of 100 x 80 mm, and then side-sealed. 3) The electrolyte was injected into the pouch in an amount of 1 g, and then vacuum-sealed. 4) The sealed pouch cell was pre-aged for 1 day. 5) The pre-aged pouch cell was heated / pressurized at 5 kgf / cm2for 10 minutes by a jig configured to fix the pre-aged pouch cell.

[0135] Life Characteristics of the Battery

[0136] <Manufacture of a secondary battery>

[0137] First, a cobalt lithium-based composite oxide, a conductive material (Denka black), and a binder (PVdF) were weighed in a weight ratio of 95:2.5:2.5, these ingredients were introduced into N-methyl pyrrolidone (NMP) and mixed to prepare a cathode mixture. The cathode mixture was coated on an aluminum foil having a thickness of 20 to 200 μm, and then pressure- and dried to obtain a cathode.

[0138] Lithium metal was used as the anode, and a carbonate-based electrolyte was prepared by dissolving 1M LiPF6 in a mixed solvent containing ethyl carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 1:1.

[0139] The separator according to each of Examples 1-3 and Comparative Examples 1-3 was interposed between the cathode and the anode, the resulting structure was accommodated in a pouch case, and an electrolyte was injected thereto, and then sealed to obtain a secondary battery.

[0140] <Test method>

[0141] Each secondary battery was first charged / discharged at 0.1C in a voltage range of 3.0-4.4V at 25℃ in a chamber, and a life characteristic test of 300 cycles was performed while charging at 1.0C and discharging at 1.0C. Here, the life characteristic was expressed as a capacity retention rate obtained by calculating the ratio of the discharge capacity after 300 cycles based on the discharge capacity of the first cycle. The results are shown in Table 1 below.

[0142] [Table 1]

[0143]

[0144] Referring to Table 1, each of the separators according to Examples 1-3 using core-shell type polymer particles having a core part and a shell part different from each other in glass transition temperature and containing a polymer grafted to the surface of the shell part as the binder polymer provided a battery having a significantly improved life characteristic and showed a significantly improved adhesion to the electrode (cathode) under a condition of wetting with an electrolyte compared to the separators according to Comparative Examples 1-3.

Claims

1. A partition, comprising: Porous polymer substrate; and A porous coating is disposed on at least one surface of a porous polymer substrate and comprises a plurality of inorganic particles and an adhesive polymer partially or wholly disposed on the surface of the inorganic particles to interconnect and fix the inorganic particles. The adhesive polymer comprises core-shell polymer particles having a core portion and a shell portion surrounding the core portion. The core polymer contained in the core portion and the shell polymer contained in the shell portion have different glass transition temperatures, and A polymer containing components that can be eluted with an electrolyte and linked by chemical bonds is grafted onto the surface of the shell portion. Based on the total weight of the core-shell polymer particles, the content of the polymer grafted onto the surface of the shell portion is 1-30% by weight. The T between the core polymer and the shell polymer g The temperature difference is 10℃-200℃. The polymer grafted onto the surface of the shell portion includes polyvinyl alcohol (PVA) or a copolymer thereof, polyethylene glycol (PEG) or a copolymer thereof, polypropylene glycol (PPG) or a copolymer thereof, polyvinyl acetate (PVAc) or a copolymer thereof, polyacrylonitrile (PAN) or a copolymer thereof, or two or more thereof.

2. The partition according to claim 1, wherein the glass transition temperature of the core polymer is higher than that of the shell polymer.

3. The partition according to claim 2, wherein the glass transition temperature of the core polymer is 85°C or higher, and the glass transition temperature of the shell polymer is -100°C to 20°C.

4. The partition according to claim 2, wherein the core polymer comprises polystyrene, polystyrene copolymer, polymethyl methacrylate, polymethyl methacrylate copolymer, polyamide polymer, or two or more thereof, and the shell polymer comprises acrylate polymer, rubber polymer, urethane polymer, silicone polymer, or two or more thereof.

5. The partition according to claim 1, wherein the glass transition temperature of the core polymer is lower than the glass transition temperature of the shell polymer.

6. The separator according to claim 5, wherein the glass transition temperature of the core polymer is from -100°C to 20°C, and the glass transition temperature of the shell polymer is 85°C or higher.

7. The partition according to claim 5, wherein the core polymer comprises an acrylate polymer, a rubber polymer, a urethane polymer, a silicone polymer, or two or more thereof, and the shell polymer comprises a polystyrene polymer, a poly(meth)acrylate polymer, a polyamide polymer, or two or more thereof.

8. The separator according to claim 1, wherein the average particle size of the core-shell polymer particles is from 100 nm to 1 μm.

9. The partition according to claim 1, wherein the average particle size of the core portion is 50%-90% of the average particle size of the core-shell polymer particles.

10. The partition according to claim 1, wherein the core-shell polymer particles comprise 100 parts by weight of the core portion and 100-300 parts by weight of the shell portion.

11. The separator according to claim 1, wherein the core-shell polymer particles comprise: The shell polymer is a core-shell polymer particle having a higher glass transition temperature than the core polymer; the shell polymer is a core-shell polymer particle having a lower glass transition temperature than the core polymer; or both.

12. The separator according to claim 1, wherein the porous polymer substrate is a polyolefin-based porous polymer substrate.

13. An electrochemical device comprising a cathode, an anode, and a partition disposed between the cathode and the anode, wherein the partition is the same as that defined in any one of claims 1 to 12.

14. The electrochemical device according to claim 13, wherein the electrochemical device is a lithium secondary battery.

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