Separator for secondary battery comprising polymer protective layer and manufacturing method therefor

Abstract

The present invention relates to a separator for a secondary battery, comprising a polymer protective layer, and a manufacturing method therefor. By coating a porous substrate with a polymer monomer or a copolymer in a single layer or multiple layers, according to the present invention, a separator for a secondary battery, comprising a polymer protective layer having increased heat resistance and wettability, may be manufactured. In addition, according to the present invention, the polymer protective layer is uniformly applied while maintaining pores in the surface of the porous substrate, thus having an effect of increasing heat resistance and wettability while maintaining the characteristics of existing separators on an equal or better level, and thus is expected to be usefully applicable to the separator for a secondary battery.

Description

Separator for secondary battery including polymer protective layer and method for manufacturing same

[0001] The present invention relates to a secondary battery separator including a polymer protective layer and a method for manufacturing the same, and more specifically, to a secondary battery separator including a polymer protective layer having enhanced heat resistance and wettability by coating a porous substrate with a single layer or multiple layers of a polymer monomer or copolymer, and a method for manufacturing the same.

[0002] Lithium-ion batteries, consisting of a cathode / anode / separator / electrolyte, are high-energy-density energy storage devices capable of reversibly converting chemical and electrical energy and rechargeable and dischargeable. They are widely used in small electronic devices such as mobile phones and laptops. Recently, their application in hybrid electric vehicles (HEVs), plug-in electric vehicles (plug-in EVs), e-bikes, and energy storage systems (ESS) has been rapidly expanding due to environmental concerns, high oil prices, and concerns about energy efficiency and storage.

[0003] Secondary batteries are stable electrochemical devices with a positive and negative electrode separated by a separator. However, due to internal or external battery abnormalities or impacts, a short circuit between the positive and negative electrodes can occur, potentially resulting in overheating and explosion. Therefore, ensuring the thermal / chemical safety of the separator as an insulator is the most important consideration.

[0004] Polyolefin-based separators, which are widely used commercially in secondary batteries, are porous films that function to prevent electrical short-circuiting between the positive and negative electrodes while providing pores that serve as passageways for lithium ions. Polyolefin-based separators are widely used commercially. However, when the battery is subjected to internal or external stimuli such as temperatures exceeding 130℃, polyolefin-based porous separators inevitably experience volume changes such as shrinkage or melting of the separator, which can lead to electrical short-circuiting between the positive and negative electrodes, which can cause explosions. Furthermore, if the separator ruptures due to dendrite growth within the battery, this can also lead to an internal short-circuit, which can lead to a battery explosion. Therefore, the development of separators that can secure excellent battery characteristics is urgently needed.

[0005]

[0006] The technical problem to be solved by the present invention is to provide a secondary battery separator having excellent mechanical strength while improving heat resistance and wettability.

[0007] Another technical problem to be solved in the present invention is to provide a method for manufacturing the above-mentioned secondary battery separator.

[0008] In addition, another technical problem to be solved in the present invention is to provide a lithium ion secondary battery including the above secondary battery separator.

[0009] In order to solve the above-mentioned technical problem, the present invention provides a secondary battery separator characterized in that a polymer protective layer is coated on the surface of a porous substrate for a secondary battery separator.

[0010] Preferably, the polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate, It is characterized by being composed of one or more monomers selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

[0011] The copolymer is characterized by being at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA).

[0012] Preferably, the polymer protective layer is Al2O x , SiO x and TiO x It may additionally include one or more inorganic substances selected from the group consisting of (X is a number from 1 to 10).

[0013] Preferably, the polymer protective layer may be formed of a single layer or multiple layers.

[0014] Preferably, the thickness of the polymer protective layer is characterized by being 1 to 1,000 nm.

[0015] Preferably, the thickness deviation of the polymer protective layer is less than 20%, more preferably less than 5%.

[0016] Preferably, the separator may be additionally coated with a ceramic coating layer.

[0017] The above ceramic coating layer may be coated on the surface of a porous substrate; or may be coated on the surface or intermediate layer of a polymer protective layer.

[0018] Preferably, the polymer protective layer is characterized in that it is formed by a dry polymer vapor deposition method.

[0019] Preferably, the polymer protective layer is characterized by having a surface coverage ratio (Rsc, polymer-coated area / membrane surface area) of 95% or more on the surface of the porous substrate.

[0020] In order to solve the other technical problems mentioned above, the present invention provides a method for manufacturing a secondary battery separator including a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of a porous substrate using a dry polymer vapor deposition method.

[0021] Preferably, the process of coating the polymer protective layer is characterized by being performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

[0022] In addition, in order to solve the other technical problems mentioned above, the present invention provides a lithium ion secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the separator is a separator including a polymer protective layer.

[0023] In this way, according to the present invention, a secondary battery separator including a polymer protective layer with enhanced heat resistance and wettability can be manufactured by coating a porous substrate with a single or multiple layers of a polymer monomer or copolymer. Furthermore, according to the present invention, since the polymer protective layer is uniformly coated while maintaining the pores of the surface of the porous substrate, the properties of existing separators are maintained at least equal to or higher than those of existing separators, while enhancing heat resistance and wettability, and thus, it is expected that the present invention can be usefully applied to secondary battery separators.

[0024] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0025] Figure 1 illustrates a form in which a polymer membrane is coated on a porous substrate according to the present invention.

[0026] Figure 2 illustrates an example in which a polymer protective layer is coated in three layers on a porous substrate according to the present invention.

[0027] FIG. 3 illustrates an example in which a polymer protective layer is coated on a separator coated with a ceramic layer according to the present invention.

[0028] FIG. 4 illustrates an example in which a ceramic layer is coated on a separator coated with a polymer protective layer according to the present invention.

[0029] FIG. 5 illustrates an example in which a ceramic layer is coated on a separator coated with a polymer protective layer according to the present invention, and then a polymer protective layer is coated again.

[0030] Figure 6 is a FE-SEM analysis image photograph of a separator coated with a polymer protective layer according to the present invention.

[0031] Figure 7 is a TEM image photograph of a separator coated with a polymer protective layer according to the present invention (Example 2).

[0032] Figure 8 shows the change in contact angle of a separator coated with a polymer protective layer according to the present invention (Example 1) compared to a porous substrate.

[0033] Figure 9 is a graph showing the TMA (Thermomechanical Analyzer) measurement results of a separator coated with a polymer protective layer according to the present invention (Example 2) compared to a porous substrate.

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different embodiments and is not limited to the embodiments described herein.

[0035] The present invention provides a secondary battery separator characterized in that a polymer protective layer is coated on the surface of a porous substrate for a secondary battery separator.

[0036] Figure 1 illustrates a form in which a polymer membrane is coated on a porous substrate according to the present invention.

[0037] “Coating on the surface of a porous substrate” as used in the present invention means coating all surfaces of the outer and inner sides of the porous substrate.

[0038] The term "porous substrate" used in the present invention refers to a sheet, film or non-woven fabric having micropores formed through which lithium ions can move.

[0039] The porous substrate may be at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, and polyethylenenaphthalene, and preferably may be polyolefin, for example, polyethylene or polypropylene.

[0040] The porous substrate may have a thickness of 1 to 100 μm. If the thickness of the porous substrate is less than 1 μm, there may be a problem that the mechanical properties may deteriorate or the battery may be damaged during charging and discharging. If the thickness of the porous substrate exceeds 100 μm, there may be a problem that the battery capacity may decrease due to the thick separator thickness.

[0041] The size and air permeability of the pores formed in the porous substrate are not particularly limited, but preferably, the pore size may be 10 nm to 10 μm, and the air permeability may be 50 to 60 sec / 100 ml.

[0042] According to the present invention, the polymer protective layer coated on the porous substrate is a multifunctional protective layer made of an acrylate polymer that improves the hydrophilicity, water repellency, heat resistance, strength, and ionic conductivity of the separator, and imparts chemical stability.

[0043] According to one embodiment of the present invention, the polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate, It is characterized by being at least one monomer selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

[0044] The above copolymer can be manufactured by selecting and combining two or more of the above monomers, and there are no special restrictions on the selection and combination thereof. Specifically, for example, it may be at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), and in particular, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) and 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) are preferred, but are not particularly limited thereto.

[0045] The above polymer protective layer may be composed of a copolymer using two or more monomers, and the proportion of each polymer constituting the copolymer is 1 to 99%, preferably 10 to 90%, but is not limited thereto.

[0046] These copolymers can be composed of monomer combinations of polymers with different roles, such as hydrophilicity, water repellency, and enhanced bonding, allowing for the design of desired properties. For example, a copolymer with a precise surface energy can be designed by combining hydrophilic and water repellent monomers, and used as a polymer protective layer, but this is not limited to this.

[0047] According to one embodiment of the present invention, the polymer protective layer may be formed of a single layer or multiple layers, and preferably may be formed of 1 to 3 layers. Specifically, it may be formed of a first polymer protective layer coated on the surface of a porous substrate, a second polymer protective layer coated on the surface of the first polymer protective layer, and a third polymer protective layer coated on the surface of the second polymer protective layer.

[0048] Figure 2 illustrates an example in which a polymer protective layer is coated in a multilayer of three layers on a porous substrate according to the present invention.

[0049] According to a specific embodiment of the present invention, each of the layers may be formed of polymer layers having different functions. Specifically, for example, the first polymer protective layer close to the surface of the separator may be formed of a polymer having a siloxane bond for improving bonding strength with the porous substrate, the second polymer protective layer coated thereon may be formed of a high heat-resistant polymer for improving heat resistance, and the third polymer protective layer coated thereon may be formed of a surface energy-controlled polymer for improving wettability with the electrolyte.

[0050] According to one embodiment of the present invention, the first polymer protective layer may be at least one selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimenylcyclosiloxane, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) and 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and in particular, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) or 2-Hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) is preferred.

[0051] The polymer constituting the first polymer protective layer as described above is a polymer having a siloxane bond and can improve bonding strength with the porous substrate.

[0052] According to one embodiment of the present invention, the second polymer protective layer may be at least one selected from the group consisting of 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), and in particular, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) or ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA).

[0053] The polymer constituting the second polymer protective layer as described above can maintain or improve the rigidity of the separator.

[0054] According to one embodiment of the present invention, the third polymer protective layer may be at least one selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 4-vinyl-pyridine, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) and glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), and in particular, may be 2-hydroxyethyl methacrylate (HEMA) or glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA).

[0055] The polymer constituting the third polymer protective layer as described above can improve the adhesive strength between the separator and the electrode, and can improve the wettability with the electrolyte by changing the surface energy of the separator.

[0056] According to one embodiment of the present invention, the polymer protective layer may further include an inorganic material, and the inorganic material may be made of a metal oxide, for example, Al2O x , SiO x and TiO x(X is an integer from 1 to 10) may include one or more selected from the group consisting of. By adding such a thinly coated inorganic material, the heat resistance of the separator can be further improved. In addition, in the case of a single layer of inorganic coating, the coating layer may be damaged in the case of a thick coating due to brittleness, but in the case of the present invention, since a polymer coating layer that can reinforce the brittleness of the inorganic material can be added, there is an advantage in that damage to the inorganic coating layer can be minimized when deformation of the separator occurs.

[0057] According to one embodiment of the present invention, a single-layer or multi-layer polymer protective layer can be formed by a dry polymer vapor deposition method, and this dry polymer vapor deposition method can be an initiator-based chemical vapor deposition (iCVD), but is not particularly limited thereto.

[0058] The above "iCVD" refers to a process that causes polymerization of monomers by decomposing a gaseous initiator into radicals. In this iCVD process, the deposition of a polymer protective layer occurs by supplying energy such as a heated filament heat source or UV.

[0059] As the above initiator, a peroxide such as tert-butyl peroxide (TBPO) or benzophenone can be used. TBPO is a volatile substance with a boiling point of about 110°C, and is thermally decomposed at around 150°C to form radicals, and benzophenone is decomposed by light such as UV to form radicals.

[0060] According to one embodiment of the present invention, the process of coating the polymer protective layer can be performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr, for example, it can be performed for 30 minutes under conditions of a temperature of 20°C and a pressure of 200 mTorr.

[0061] If the above coating temperature is less than 10°C, the composition of the coating equipment becomes complicated and the manufacturing cost increases, which is a disadvantage, and if the above coating temperature exceeds 80°C, the adsorption of the monomer is not easy.

[0062] If the coating pressure is less than 1 mTorr, the reaction speed may be too slow, and if the coating pressure exceeds 500 Torr, it may be difficult to activate the initiator.

[0063] If the coating time is less than 1 minute, the desired coating thickness of the polymer protective layer cannot be reached, and if the coating time exceeds 600 minutes, the coating thickness may become too thick, which may reduce the breathability of the separator.

[0064] According to one embodiment of the present invention, the polymer protective layer may have a surface coverage ratio (Rsc, polymer-coated area / membrane surface area) of 95% or more on the surface of the porous substrate, and may uniformly and evenly coat the inner surface of the pores formed within the porous substrate.

[0065] In the present invention, the polymer protective layer can maintain the pore structure of the porous substrate and the porous substrate's air permeability even when coated in a single or multi-layer manner. Specifically, after coating the polymer protective layer according to the present invention, the difference in air permeability of the separator can be less than 10%, preferably less than 5%, and more preferably less than 3%.

[0066] According to one embodiment of the present invention, the thickness of the polymer protective layer may be 1 to 1,000 nm, preferably 3 to 100 nm. In this case, if the thickness of the polymer protective layer is less than 1 nm, the mechanical strength and physicochemical properties may be reduced, and if the thickness of the polymer protective layer exceeds 1,000 nm, there is a problem that the volume of the secondary battery increases and ion mobility decreases.

[0067] According to one embodiment of the present invention, the polymer protective layer can be uniformly and smoothly coated, and specifically, the polymer protective layer coated on the surface of the porous substrate can have a thickness variation of less than 20%, preferably less than 5%, and more preferably less than 1%. In this case, if the thickness variation of the polymer protective layer exceeds 20%, the performance of the separation membrane, ion mobility, etc., can be reduced.

[0068] According to one embodiment of the present invention, the total thickness of the separator coated with the polymer protective layer may be 10 nm to 500 μm, preferably 1 μm to 100 μm, and the total thickness of the separator may be controlled depending on the thickness of the polymer protective layer.

[0069] According to one embodiment of the present invention, by coating the polymer protective layer on a porous substrate, the separator can have a contact angle lower than that of the porous substrate. Specifically, the contact angle of a typical porous substrate is 90 to 105°, and the contact angle of the separator coated with the polymer protective layer according to the present invention can be reduced to 40 to 60°. The separator of the present invention having such a reduced contact angle can have improved wettability with respect to an electrolyte.

[0070] According to one embodiment of the present invention, the separator may be additionally coated with a ceramic coating layer, which may improve the thermal stability of the separator under conditions of high temperature or overcharge, thereby enhancing the safety of the secondary battery with respect to preventing internal short circuits.

[0071] The above ceramic coating layer may be coated before the polymer protective layer is coated on the porous substrate or may be coated after the polymer protective layer is coated on the porous substrate.

[0072] Therefore, a separator coated on the surface of a porous substrate including the ceramic coating layer or coated on the surface or intermediate layer of a polymer protective layer may also be included in the scope of the present invention.

[0073] FIG. 3 illustrates an example of a process in which a ceramic coating layer is coated on a porous substrate and then a polymer protective layer is coated according to the present invention.

[0074] FIG. 4 illustrates an example of a process in which a polymer protective layer is coated on a porous substrate and then a ceramic coating layer is coated according to the present invention.

[0075] The above ceramic coating layer can be coated to a thickness of 0.1 to 10 μm, preferably to a thickness of 0.5 to 7 μm, and more preferably to a thickness of 1 to 4 μm.

[0076] The above ceramic coating layer may be formed of inorganic material particles having strong mechanical properties and excellent properties at high temperatures, and the properties of these ceramic particles can prevent deformation and destruction of the separator due to physicochemical changes occurring within the secondary battery. The inorganic material particles may use at least one selected from the group consisting of TiO2, SiO2, SnO2, CeO2, ZrO2, CaCO3, BaCO3, Al2O3, Al(OH)3, and Mg(OH)2, and the average particle diameter of the inorganic material particles may be 10 nm to 10 μm, preferably 5 nm to 50 μm, but is not limited thereto.

[0077] The above ceramic coating layer may be formed of a single layer or multiple layers.

[0078] The present invention provides a method for manufacturing a separator for a secondary battery including a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of a porous substrate using a dry polymer vapor deposition method.

[0079] According to one embodiment of the present invention, the process of coating the polymer protective layer is characterized in that it is performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

[0080] When the above polymer protective layer is formed in multiple layers, the method may include a step of coating a first polymer protective layer on the surface of a porous substrate, a step of coating a second polymer protective layer on the porous substrate coated with the first polymer protective layer, and a step of coating a third polymer protective layer on the porous substrate coated with the second polymer protective layer.

[0081] In addition, the present invention provides a lithium ion secondary battery including a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte, wherein the separator is a separator including a polymer protective layer.

[0082] The lithium-ion secondary battery of the present invention can be manufactured using conventional methods known in the art, without any particular limitations. For example, it can be manufactured by assembling a separator coated with a polymer protective layer according to the present invention between the positive and negative electrodes, and then injecting an electrolyte.

[0083] The method for manufacturing the electrode is not particularly limited, and the negative electrode material or positive electrode material can be manufactured in a form in which it is bonded to the electrode current collector according to a conventional method known in the art.

[0084] The cathode material may be a conventional one, and for example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a composite oxide formed by a combination thereof may be used.

[0085] The negative electrode material may be a conventional negative electrode material, and may be, for example, a lithium adsorbent such as lithium metal or a lithium alloy, carbon, petroleum coke, activated carbon, graphite, or other carbons.

[0086] The electrolyte is A + B - As a salt with the same structure, A + is Li + , Na+ , K + B containing an ion composed of an alkali metal cation or a combination thereof; - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO - , NCF3(SO2)2 - , CCF2(SO2)3 - Salts containing anions such as or combinations thereof are dissolved or dissociated in organic solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone) or mixtures thereof, but are not limited thereto.

[0087] Electrolyte injection can be performed at an appropriate stage during the battery manufacturing process, depending on the final product's manufacturing process and required properties. This can be done before battery assembly or during the final stage of battery assembly.

[0088] In this way, according to the present invention, a secondary battery separator including a polymer protective layer with enhanced heat resistance and wettability can be manufactured by coating a porous substrate with a single or multiple layers of a polymer monomer or copolymer. Furthermore, according to the present invention, since the polymer protective layer is uniformly coated while maintaining the pores of the surface of the porous substrate, the properties of existing separators are maintained at least equal to or higher than those of existing separators, while enhancing heat resistance and wettability, and thus, it is expected that the present invention can be usefully applied to secondary battery separators.

[0089]

[0090] Hereinafter, the present invention will be described in more detail using examples. These examples are intended solely to illustrate the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

[0091] <Manufacturing Example 1> Manufacturing of a porous substrate

[0092] HDPE (high density polyethylene) with a molecular weight (Mw) of 300,000 to 500,000 and liquid paraffin were mixed in a weight ratio of 35:65 and melted and extruded through an extruder to obtain an unstretched sheet having a thickness of approximately 800 to 1200 μm. The unstretched sheet was then stretched 5 times in the MD direction and 5 times in the TD direction at 105°C to 120°C. Subsequently, liquid paraffin was extracted using methylene chloride at room temperature. Subsequently, heat-setting was performed at a temperature of 128°C to 132°C for 30 seconds to 2 minutes to obtain a porous substrate (thickness 9 μm) having micropores formed therein.

[0093]

[0094] <Example 1> Manufacturing of a separator coated with a polymer protective layer

[0095] 100 mL each of monomer 2-hydroxyethyl methacrylate (HEMA) (Merck, 96%) and initiator tert-Butyl peroxide (Merck, 98%) were charged into an iCVD coating device equipped with a monomer canister and an initiator canister, and then the monomer canister was heated to about 50°C and the initiator canister was heated to about 40°C.

[0096] Afterwards, the porous substrate was placed in the coating effective area within the coating equipment, the temperature was set to 25°C, and a vacuum was maintained. To activate the initiator, the filament temperature was heated to approximately 150°C, and the coating area and the canister were evacuated. Then, while maintaining the pressure in the coating area at approximately 200 mTorr, the monomer and initiator were supplied to form a first polymer protective layer on the porous substrate. At this time, the thickness of the polymer protective layer was 60 nm.

[0097]

[0098] <Example 2>

[0099] A separator having a polymer protective layer formed thereon was manufactured in a similar manner to Example 1, but 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) was used instead of 2-hydroxyethyl methacrylate (HEMA) to manufacture a separator coated with a first polymer protective layer. The thickness of the polymer protective layer coated on the surface of the porous substrate was 30 nm.

[0100]

[0101] <Example 3> Manufacturing of a separator with a two-layer polymer protective layer

[0102] In Example 2, a second polymer protective layer was coated on the surface of a porous substrate using glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) on the first polymer protective layer coated on the surface of the porous substrate using 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), thereby manufacturing a separator having two polymer protective layers.

[0103] At this time, the coating process of the second polymer protective layer was performed in the same manner as the coating process of the first polymer protective layer. The thickness of the polymer protective layer coated on the surface of the porous substrate was 60 nm.

[0104]

[0105] <Example 4> Manufacturing of a separator including a ceramic coating layer

[0106] A ceramic coating layer was formed by mixing a porous substrate with a binder using ceramic powder to form a slurry, dip-coating the slurry, and drying it in a hot air oven. A separator coated with a polymer protective layer using glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) on the ceramic coating layer was manufactured. The polymer protective layer coated on the surface of the porous substrate had a thickness of 100 nm.

[0107]

[0108] <Example 5> Manufacturing of a separator with a three-layer polymer protective layer

[0109] In Example 2, a first polymer protective layer was coated on the surface of a porous substrate using 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), a second polymer protective layer was coated using ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), and then a third polymer protective layer was coated using 2-hydroxyethyl methacrylate (HEMA), thereby manufacturing a separator having three polymer protective layers.

[0110] At this time, the coating process of the second polymer protective layer and the third polymer protective layer was performed in the same manner as the coating process of the first polymer protective layer.

[0111] The thickness of the polymer protective layer coated on the porous substrate surface was 60 nm.

[0112]

[0113] <Example 6> Manufacturing of a separator with a three-layer polymer protective layer formed on a ceramic coating layer

[0114] A porous substrate was coated with ceramic powder, and then a first polymer protective layer was coated on the ceramic coating layer using 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), a second polymer protective layer was coated on the ceramic coating layer using ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), and then a third polymer protective layer was coated on the porous substrate using 2-hydroxyethyl methacrylate (HEMA), thereby manufacturing a separator having a ceramic coating layer and three polymer protective layers.

[0115]

[0116] <Example 7> Manufacturing of a separator including a ceramic coating layer

[0117] A separator was manufactured by coating the surface of a porous substrate with glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) to form a first polymer protective layer, and then forming a ceramic coating layer thereon using ceramic powder. The thickness of the polymer protective layer coated on the surface of the porous substrate was 30 nm.

[0118]

[0119] <Example 8> Manufacturing of a separator with a three-layer polymer protective layer

[0120] In Example 2, a first polymer protective layer was coated on the surface of a porous substrate using 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), a second polymer protective layer was coated using 2-hydroxyethyl methacrylate (HEMA), and then a third polymer protective layer was coated using ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), thereby manufacturing a separator having three polymer protective layers. The thickness of the polymer protective layer coated on the surface of the porous substrate was 30 nm.

[0121]

[0122] <Comparative Example 1>

[0123] The porous substrate manufactured in the above manufacturing example 1 was used as a base film.

[0124]

[0125] Comparative Example 2

[0126] A separator was manufactured by forming a ceramic coating layer on the porous substrate of Comparative Example 1.

[0127]

[0128] <Battery Manufacturing>

[0129] 1M LiPF6 in EC / DEC (3:7 v / v) and 5% FEC electrolyte, Super P (1 wt%) conductive agent, CMC (1.5 wt%), SBR (2.5 wt%) binder, cross-section 5.399 mg / cm 2 The cell was manufactured with 0.5T Space and 2032 Coin Cell electrode size under the conditions of loading level, Li metal (700 ㎛) positive electrode material, natural graphite negative electrode material, and composite density of 1.46 g / cc.

[0130]

[0131] <Test Example 1> Formation and component analysis of a polymer protective layer

[0132] In order to confirm the formation of a polymer protective layer in a separator having a polymer protective layer coated on a porous substrate surface according to the present invention, FE-SEM analysis was performed.

[0133] Figure 6 is a FE-SEM analysis image photograph of a separator coated with a polymer protective layer according to the present invention. As can be seen here, it was confirmed that the polymer protective layer was well formed and pores were maintained in the separators of Examples 1 to 4 and Example 7.

[0134] Figure 7 is a TEM image photograph of a separator coated with a polymer protective layer according to the present invention (Example 2). As can be seen here, it can be confirmed that the polymer protective layer is evenly and uniformly coated to the inner surface of the pores present in the porous substrate, and that the polymer protective layer is composed of components of C, O, and Si.

[0135]

[0136] <Test Example 2> Membrane Characteristics Evaluation

[0137] According to the present invention, the thickness, air permeability, adhesive strength, heat shrinkage, and TMA properties of a separator having a polymer protective layer coated on a porous substrate surface were evaluated and are shown in Table 1 below.

[0138] Specifically, the thickness of the separator was measured by cutting the separator and measuring the cross-section using FE-SEM, the air permeability was measured by measuring the time required to pass 100 mL of air through the separator, the adhesive strength was measured by pressing the cathode coated with the cathode material and the separator coated with the polymer protective layer at a temperature of 70℃ while applying pressure, and then performing a 180℃ peel test using a universal material testing machine, and the thermal shrinkage was calculated as the area reduced compared to the initial area after exposing it for 30 minutes in a box oven maintained at a temperature of 130℃.

[0139] TMA measured the displacement of the membrane in an environment where the temperature was increased while pulling the membrane with a load of 0.005 N, and measured the temperature at which the membrane broke, at which the displacement changed rapidly.

[0140]

[0141] Figure 8 shows the change in contact angle of a separator coated with a polymer protective layer according to the present invention (Example 1) compared to a porous substrate.

[0142] As can be seen from the results in Table 1 and Fig. 8, it was confirmed that the separator coated with a polymer protective layer according to the present invention had a reduced contact angle, and thus improved wettability.

[0143] Figure 9 is a graph showing the TMA (Thermomechanical Analyzer) measurement results of a separator coated with a polymer protective layer according to the present invention (Example 2) compared to a porous substrate.

[0144] As shown in Table 1 and Fig. 9, the porous substrate without a polymer protective layer broke at 151.6°C, while the separator coated with a polymer protective layer according to the present invention broke at 210.33°C. From this, it was confirmed that the separator coated with a polymer protective layer according to the present invention had improved thermal stability.

[0145]

[0146] <Test Example 3> Characteristic Evaluation of a Battery Using a Separator

[0147] According to the present invention, a cell was manufactured using a separator having a polymer protective layer coated on the surface of a porous substrate, and then its characteristics were analyzed. The results are shown in Table 2 below.

[0148]

[0149] As shown in Table 2 above, as a result of confirming whether a significant difference in electrode life occurred over 100 cycles, it was confirmed that the separator of Example 2 having a polymer protective layer coated on the surface of a porous substrate according to the present invention showed initial discharge capacity, initial efficiency, and life characteristics equivalent to or higher than those of the porous substrate of Comparative Example 1. From this, it can be seen that the separator having a polymer protective layer coated on the surface of a porous substrate according to the present invention maintains the characteristics equivalent to or higher than those of a conventional separator while providing additional functionality such as heat resistance and wettability.

[0150] While specific aspects of the present invention have been described in detail above, it should be apparent to those skilled in the art that these specific descriptions are merely preferred embodiments and do not limit the scope of the present invention. Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

[0151]

[0152] In this way, according to the present invention, a secondary battery separator including a polymer protective layer with enhanced heat resistance and wettability can be manufactured by coating a porous substrate with a single or multiple layers of a polymer monomer or copolymer. Furthermore, according to the present invention, since the polymer protective layer is uniformly coated while maintaining the pores of the surface of the porous substrate, the properties of existing separators are maintained at least equal to or higher than those of existing separators, while enhancing heat resistance and wettability, and thus, it is expected that the present invention can be usefully applied to secondary battery separators.

Claims

1. A secondary battery separator coated with a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of a porous substrate for a secondary battery separator.

2. In paragraph 1, The above polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate and A secondary battery separator coated with a polymer protective layer, characterized in that it is composed of one or more monomers selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

3. In paragraph 2, A secondary battery separator coated with a polymer protective layer, characterized in that the copolymer is at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA).

4. In paragraph 1, The above polymer protective layer is Al2O x , SiO x and TiO x A secondary battery separator coated with a polymer protective layer, characterized in that it additionally includes one or more inorganic substances selected from the group consisting of (X is a number from 1 to 10).

5. In paragraph 1, A secondary battery separator coated with a polymer protective layer, characterized in that the polymer protective layer is composed of a single layer or multiple layers.

6. In paragraph 1, A secondary battery separator coated with a polymer protective layer, characterized in that the thickness of the polymer protective layer is 1 to 1,000 nm.

7. In paragraph 6, A secondary battery separator coated with a polymer protective layer, characterized in that the thickness deviation of the polymer protective layer is less than 20%.

8. In paragraph 1, A secondary battery separator coated with a polymer protective layer, characterized in that the separator further includes a ceramic coating layer.

9. In paragraph 8, A secondary battery separator coated with a polymer protective layer, characterized in that the ceramic coating layer is coated on the surface of a porous substrate; or coated on the surface or intermediate layer of a polymer protective layer.

10. In paragraph 1, A secondary battery separator coated with a polymer protective layer, characterized in that the polymer protective layer is formed by a dry polymer vapor deposition method.

11. In paragraph 1, A secondary battery separator coated with a polymer protective layer, characterized in that the polymer protective layer has a surface coverage ratio (Surface coverage ratio (Rsc, polymer-coated area / separator surface area) of 95% or more on the surface of a porous substrate.

12. A method for manufacturing a secondary battery separator coated with a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of a porous substrate using a dry polymer vapor deposition method.

13. In paragraph 12, A method for manufacturing a secondary battery separator coated with a polymer protective layer, characterized in that the process of coating the polymer protective layer is performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

14. In a lithium ion secondary battery including a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte, A lithium ion secondary battery, characterized in that the separator is a secondary battery separator coated with a polymer protective layer according to any one of claims 1 to 11.

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