Hybrid separator and lithium secondary battery including same

Abstract

The present invention relates to a hybrid separator and a lithium secondary battery comprising the same. As one embodiment, the present invention relates to a lithium secondary battery comprising a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a liquid electrolyte, the separator being a hybrid separator comprising a porous substrate and a flexible polymer layer, the flexible polymer layer is arranged on at least one surface of the porous base material and can conduct lithium ions, and the lithium ion conductivity of the mixed diaphragm is 10 <-4 >-10 <-2 > S / cm. The hybrid separator according to the present invention comprises the flexible polymer layer, and thus has the effects of excellent mechanical strength of the separator and significantly reduced generation of lithium dendrites during charging and discharging.

Description

Technical Field

[0001] The invention relates to a hybrid diaphragm and a lithium secondary battery comprising the hybrid diaphragm. Background Art

[0002] In recent years, lithium secondary batteries have been increasingly being used for higher capacity and larger size in order to be used in electric vehicles, etc. In order to achieve high capacity with the same volume, thinning is required, and ensuring battery safety has become a very important factor.

[0003] Lithium secondary batteries generally include a separator disposed between a positive electrode and a negative electrode, and the separator uses a polyolefin-based porous film. The polyolefin-based porous film has pores through which lithium ions can pass, but lithium ion enrichment occurs during repeated charge / discharge processes, thereby forming lithium dendrites in the negative electrode, and the formed lithium dendrites may cause various problems in the battery.

[0004] Specifically, when lithium dendrites are formed, they grow into sharp needles. When the lithium dendrites grown as described above block the pores of the polyolefin-based porous membrane or pierce the polyolefin-based porous membrane, they become the cause of internal short circuits in the battery, which may cause stability problems such as fire.

[0005] In addition, when the surface of the newly grown lithium dendrite is exposed to the electrolyte, the electrolyte and the high specific surface area lithium are easily involved in electrochemical side reactions, so the electrolyte is quickly depleted and the battery life characteristics are reduced. In addition, due to the change in electrode thickness that occurs when lithium dendrites are formed, the volume of the entire battery changes, so the dimensional stability of the battery is reduced.

[0006] In order to solve this problem, various technologies for suppressing the growth of lithium dendrites have been proposed, but currently, there is insufficient development of technologies that can improve the mechanical properties and ion conductivity of the separator while solving all the problems caused by lithium dendrites.

[0007] On the other hand, all-solid-state batteries using a solid-phase electrolyte between the positive and negative electrodes are being studied. All-solid-state batteries require a solid electrolyte that transports lithium ions. Solid electrolytes are mainly divided into organic (polymer) electrolytes and inorganic electrolytes. Polymer electrolytes transport lithium ions in molecular chains by fast movement (hopping), and compared with the combination of liquid electrolytes and separators, lithium ion enrichment is reduced, lithium dendrites cannot grow well, and therefore have excellent stability. However, in the case of polymers that do not contain liquid, the ionic conductivity at room temperature shows a very low level of about 10 -7 -10 -4S / cm. In addition, most polymers have the disadvantages of being unstable at high voltages above 4V and having poor mechanical strength. In order to achieve commercialization, the thickness of the polymer electrolyte should be as thick as 50μm or more. Therefore, even if the thickness of the battery is increased and undergoes a cross-linking process, it is very difficult for the mechanical strength of the polymer electrolyte to reach a level comparable to that of a polyolefin-based porous substrate. Moreover, it is actually difficult to apply to batteries for electric vehicles, etc., which must be thin-filmed to achieve high power and high capacity. In addition, although it may vary depending on the type of polymer used, the thermal shrinkage of the polymer electrolyte is high compared to a polyolefin-based porous substrate coated with ceramics, and battery safety may be impaired.

[0008] (Patent Document 1) Korean Patent Publication No. 10-2019-0046237 (Publication Date: May 7, 2019) Summary of the invention

[0009] 1. Technical issues to be resolved

[0010] According to one aspect of the present invention, a hybrid separator including a flexible polymer layer capable of conducting lithium ions may be provided.

[0011] According to one aspect of the present invention, a new concept hybrid membrane including a flexible polymer layer arranged on at least one side of a porous substrate and capable of conducting lithium ions and a lithium secondary battery including the hybrid membrane can be provided. The lithium secondary battery includes the hybrid membrane, thereby suppressing the growth of lithium dendrites.

[0012] According to one aspect of the present invention, a new concept hybrid separator that compensates for the disadvantages of existing separators using a polyolefin-based porous substrate and the disadvantages of a polymer electrolyte can be provided.

[0013] According to one aspect of the present invention, the ionic conductivity and mechanical physical properties of the polyolefin-based porous substrate itself are maintained unchanged without increasing the total thickness of the separator, thereby providing a thin film separator.

[0014] According to one aspect of the present invention, a hybrid separator may be provided that may significantly suppress the growth of lithium dendrites also during repeated charge / discharge processes.

[0015] According to one aspect of the present invention, a hybrid separator and a lithium secondary battery including the hybrid separator can be provided, wherein the hybrid separator has excellent lithium ion conductivity at 25° C. even if the total thickness of the separator is 50 μm or less and is a thin film, and the porosity is as low as 40% or less. The lithium ion conductivity of the hybrid separator is 10 -4 S / cm or more, 10 -3 S / cm or more, 10 -2S / cm or less, e.g. 10 -4 -10 -2 S / cm, 10 -3 -10 -2 S / cm, 4.0×10 -3 -10 -2 S / cm, 4.0×10 -3 -7.0×10 -3 S / cm.

[0016] According to one aspect of the present invention, a hybrid membrane and a lithium secondary battery comprising the hybrid membrane can be provided. Even if a flexible polymer layer is formed, the hybrid membrane has a needle puncture strength of more than 3N and a tensile strength of more than 100MPa, and has excellent mechanical and physical properties reaching the level of existing polyolefin-based porous substrates.

[0017] According to one aspect of the present invention, a hybrid membrane and a lithium secondary battery including the hybrid membrane can be provided, wherein the hybrid membrane can act as a solid electrolyte even if the liquid electrolyte is lost during repeated charge / discharge processes, thereby enabling smooth lithium migration.

[0018] The hybrid diaphragm and lithium secondary battery of the present invention can be widely used in electric vehicles, battery charging stations, other green technology fields such as solar power generation and wind power generation using batteries. In addition, the hybrid diaphragm and lithium secondary battery of the present invention can be used in eco-friendly electric vehicles and hybrid vehicles that prevent climate change by suppressing air pollution and greenhouse gas emissions.

[0019] (II) Technical solution

[0020] One embodiment of the present invention provides a lithium secondary battery, the lithium secondary battery comprising a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a liquid electrolyte, the separator being a hybrid separator comprising a porous substrate and a flexible polymer layer, the flexible polymer layer being disposed on at least one side of the porous substrate and capable of conducting lithium ions, the hybrid separator having a lithium ion conductivity of 10 at 25°C. -4 -10 -2 S / cm.

[0021] As an embodiment, a lithium secondary battery is provided, the lithium secondary battery comprising: a negative electrode; a positive electrode; a separator, the separator is arranged between the negative electrode and the positive electrode, and the separator is arranged to physically separate the positive electrode and the negative electrode while allowing ions to pass through; and a liquid electrolyte, the liquid electrolyte is arranged between the negative electrode and the positive electrode, and the liquid electrolyte is arranged to transport ions between the positive electrode and the negative electrode, wherein the separator is a hybrid separator comprising a porous substrate and a flexible polymer layer, the flexible polymer layer is arranged on at least one side of the porous substrate and can conduct lithium ions, and the lithium ion conductivity of the hybrid separator at 25°C is 10 -4 -10 -2 S / cm.

[0022] As an embodiment, the porosity of the hybrid membrane may be 40% or less, but is not limited thereto.

[0023] As an embodiment, the heat shrinkage rate of the hybrid separator at 150° C. may be 30% or less, and is not limited thereto.

[0024] As an embodiment, when the thickness of the porous substrate is set to A and the thickness of the flexible polymer layer is set to B, B / A may be 1.0 or less, and is not limited thereto.

[0025] As an embodiment, the thickness of the flexible polymer layer on each side of the hybrid separator may be 0.1-5 μm, but is not limited thereto.

[0026] As an embodiment, the porous substrate may be a polyolefin-based porous film or a composite film having an inorganic particle layer on one or both sides of the polyolefin-based porous film, and is not limited thereto.

[0027] As an embodiment, the porous substrate may have a thickness of 4-25 μm and a porosity of 30-70%, but is not limited thereto.

[0028] As an embodiment, the flexible polymer layer may be composed of a cross-linked polymer capable of conducting lithium ions, but is not limited thereto. The "flexible" is distinguished from "non-flexible" or "rigid". Moreover, "flexible" refers to a state in which it is not disposed on a porous substrate.

[0029] As an embodiment, the flexible polymer layer may include a cross-linked copolymer including a unit derived from an acrylic acid-based monomer and a unit derived from an ethylenically unsaturated multifunctional monomer, without being limited thereto.

[0030] As an embodiment, the flexible polymer layer may further include any one or two or more additives selected from lithium salts, free radical additives and high-reactivity additives.

[0031] As an embodiment, the ethylenically unsaturated multifunctional monomer may be a multifunctional acrylate-based monomer, and is not limited thereto.

[0032] As an embodiment, the ethylenically unsaturated multifunctional monomer may include one or more of 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, pentaethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyether polyol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol pentaacrylate, and is not limited thereto.

[0033] As an embodiment, the hybrid separator may have a pin puncture strength of 3N or more according to ASTM D3763_02, and a tensile strength of 150-200 MPa according to ASTM D882, but is not limited thereto.

[0034] As an embodiment, the elongation at break of the hybrid separator at 25° C. may be 20-90%, and the elastic recovery rate at 20% strain may be 50-100%, but is not limited thereto.

[0035] Another embodiment of the present invention provides a hybrid separator, the hybrid separator comprising a porous substrate and a flexible polymer layer, the flexible polymer layer being disposed on at least one side of the porous substrate and capable of conducting lithium ions, the hybrid separator having a lithium ion conductivity of 10 at 25°C. -4 -10 -2 S / cm.

[0036] As an embodiment, the porous substrate may be a polyolefin-based porous film or a composite film having an inorganic particle layer on one or both sides of the polyolefin-based porous film.

[0037] As an embodiment, the flexible polymer layer may be composed of a cross-linked polymer capable of conducting lithium ions.

[0038] As an embodiment, the flexible polymer layer may include a cross-linked copolymer including units derived from acrylic acid-based monomers and units derived from ethylene-based unsaturated polyfunctional monomers, without being limited thereto.

[0039] As an embodiment, the flexible polymer layer may further include any one or two or more additives selected from lithium salts, free radical additives and high-reactivity additives.

[0040] (III) Beneficial effects

[0041] According to one embodiment of the present invention, the ionic conductivity and mechanical strength of the polyolefin-based porous substrate can be maintained unchanged while the dendrite growth of lithium ions can be suppressed during repeated charge / discharge processes.

[0042] Furthermore, even if the amount of liquid electrolyte is lost due to the loss of a high-boiling-point organic solvent during repeated charge / discharge processes and long-term storage of the battery, the flexible polymer layer has lithium ion conductivity, which allows lithium migration to proceed smoothly, thereby maintaining battery performance for a long time. Therefore, it is possible to provide an advantage that the electrical characteristics of the battery are less changed even during long-term use.

[0043] In addition, since the flexible polymer layer having both lithium ion conductivity and flexibility is formed as a thin film, a high-capacity lithium secondary battery can be provided. That is, in order to increase the capacity of the battery, more battery cells can be stacked in the same volume, so a high-capacity lithium secondary battery can be provided. The battery cell may refer to a combination of a positive electrode, a negative electrode, and a separator disposed therebetween.

[0044] In addition, the flexible polymer layer according to one embodiment of the present invention has excellent elasticity and acts as a reinforcing material of the diaphragm, thereby having the advantage of improving the mechanical properties of the entire diaphragm. In addition, not only can the growth of lithium dendrites be suppressed, but even if lithium dendrites grow, the problem that occurs when the dendrites pierce the diaphragm can be compensated, and the elasticity can partially restore it to the original state, so that the damage to the polyolefin-based porous substrate can be minimized. Therefore, the life of the battery can be further improved, and a battery with a lower risk of explosion can be provided.

[0045] Furthermore, thermal shrinkage of the separator can be minimized, and volume change of the battery can be suppressed by alleviating thickness change during charge / discharge of the battery, so the stability of the battery can be improved.

[0046] In addition, the flexible polymer layer contains a cross-linked copolymer with lithium ion conductivity, has excellent ion conductivity, and thus can play a role similar to that of a liquid electrolyte, and has low reactivity with lithium compared to a liquid electrolyte, thereby suppressing an increase in resistance due to depletion of the liquid electrolyte and can contribute to improving battery life characteristics. DETAILED DESCRIPTION

[0047] The present invention is described in detail below, but this is merely exemplary, and the present invention is not limited to the specific embodiments described exemplarily.

[0048] In addition, unless otherwise defined, all technical terms and scientific terms have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the description of the present invention are only used to effectively describe specific embodiments and are not intended to limit the present invention.

[0049] Furthermore, unless otherwise specifically stated herein, singular forms used in the specification and the claims may also include plural forms.

[0050] Furthermore, unless otherwise specifically described to the contrary, when a part is described as “including” or “comprising” a certain component, this means that other components may also be included, rather than excluding other components.

[0051] In addition, unless specifically defined otherwise, when a layer or component is described as being “on” another layer or component, this includes not only the case where the layer or component is in contact with the other layer or component but also the case where another layer or component exists between the two layers or components.

[0052] In addition, with respect to the terms "about", "substantially", etc. used in the present invention, they are used as meanings of numerical values ​​or values ​​close to them when inherent manufacturing and material tolerances appear in the mentioned meanings, and are used to prevent the disclosure of precise or absolute numerical values ​​mentioned to aid understanding of the present invention from being unfairly used by unscrupulous infringers.

[0053] The term "(meth)acrylic acid" used in the present invention means acrylic acid or methacrylic acid.

[0054] As an embodiment, the negative electrode, positive electrode, and liquid electrolyte used in the present invention may be used without limitation as long as they are generally used in the art.

[0055] Hereinafter, each structure of the hybrid separator according to one embodiment of the present invention will be described in more detail.

[0056] [Porous substrate]

[0057] As an embodiment, the porous substrate can be used without limitation as long as it is a porous substrate commonly used in the art. More specifically, for example, the porous substrate can be a polyolefin-based porous membrane or a composite membrane, wherein the composite membrane is a composite membrane having an inorganic particle layer on one or both sides of the polyolefin-based porous membrane in which inorganic particles are connected to each other to form pores.

[0058] As an embodiment, the polyolefin-based porous membrane is a membrane or sheet commonly used in the art, and the polyolefin-based porous membrane can be, for example, a polyolefin-based porous membrane such as polyethylene, polypropylene, etc., but is not limited thereto, and all porous substrates known as porous substrates for diaphragms of electrochemical devices can be used.

[0059] As an embodiment, the thickness of the porous substrate may be 1 μm or more, 3 μm or more, 4 μm or more, 5 μm or more, 6 μm or more, 7 μm or more, 8 μm or more, 9 μm or more, 10 μm or more, 100 μm or less, 50 μm or less, 30 μm or less, 20 μm or less, 15 μm or less, 12 μm or less, and may be any value between the above values. For example, the thickness of the porous substrate may be 1-100 μm, 3-50 μm, 4-25 μm, 5-20 μm, 5-15 μm, 6-10 μm or 9-10 μm. The porous substrate may be a porous substrate manufactured by stretching, but is not limited thereto.

[0060] In addition, the porosity of the porous substrate may be 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 70% or less, 65% or less, 60% or less, and any value between the above values. For example, the porosity of the porous substrate may be 30-70%, 35-65%, 40-65%, or 45-65%.

[0061] The composite membrane as another embodiment of the porous substrate can be a composite membrane having an inorganic particle layer formed on a porous membrane composed of the polyolefin, etc. The inorganic particle layer can be an inorganic particle layer formed by coating and drying a slurry mixture formed by mixing inorganic particles and a binder so that the inorganic particles are connected to each other to form holes. The inorganic particle layer can include a binder and inorganic particles, and the inorganic particle layer can be a porous inorganic particle layer in which inorganic particles are connected and fixed by the binder to form holes.

[0062] The inorganic particles can be used without limitation as long as they are known inorganic particles added to improve the heat resistance of the separator. Although not limited thereto, for example, any one or a mixture of two or more selected from boehmite, calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, aluminum oxide, mica, zeolite, glass, etc. can be used. In addition, as inorganic particles having a dielectric constant of 5 or more, any one or a mixture of two or more selected from SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, or SiC, etc. can be used. In addition, as inorganic particles having piezoelectricity, any one or a mixture of two or more selected from BaTiO3, Pb(Zr,Ti)O3 (PZT), Pb 1- x La x Zr 1-y Ti y O3 (PLZT), PB(Mg3Nb 2 / 3 )O3-PbTiO3 (PMN-PT) or hafnia (HfO2), etc. can be used. In addition, as inorganic particles having lithium ion transport ability, any one or a mixture of two or more selected from lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4)-based glass or P2S5 (Li xP y S z , any one or a mixture of two or more of base glasses such as 0 < x < 3, 0 < y < 3, 0 < z < 7). When the high dielectric constant inorganic particles, the piezoelectric inorganic particles, and the inorganic particles having lithium ion transport ability are used in combination, their synergistic effect can be doubled.

[0063] The size of the inorganic particles is not limited, but the average particle diameter can be 0.001 μm or more, 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, 0.5 μm or more, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less, and can be any value between the above values. For example, the size of the inorganic particles can be 0.001 - 5 μm, 0.01 - 3 μm, 0.1 - 1 μm, or 0.5 - 1 μm. Within the above range, an inorganic particle layer with uniform thickness can be formed, and an appropriate porosity can be provided, but it is not limited thereto. The average particle diameter refers to D50, and D50 refers to the particle diameter corresponding to a cumulative fraction of 50% based on volume. The average particle diameter can be obtained from the particle size distribution results by sampling the particles to be measured according to the ISO 13320 - 1 standard and analyzing them using the S3500 of MICROTRAC company.

[0064] In one embodiment, the thickness of the inorganic particle layer is not limited, but can be, for example, more than 0 μm, 0.1 μm or more, 0.2 μm or more, 0.3 μm or more, 0.5 μm or more, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1.5 μm or less, 1 μm or less, or a value between the above values. For example, the thickness of the inorganic particle layer can be 0.1 μm to 5 μm, 0.2 μm to 5 μm, 0.5 μm to 5 μm, 1 μm to 4 μm, or 2 μm to 4 μm, and is not limited thereto.

[0065] In one embodiment, the inorganic particle layer can be disposed on one or both sides of the porous membrane. Based on the entire surface of the porous membrane, the area of the inorganic particle layer can be 60% or more, 70% or more, 80% or more, 90% or more, or 90 - 100%. That is, the inorganic particle layer can be formed on the entire area of the porous membrane.

[0066] In one embodiment, the inorganic particle layer can be disposed on one or both sides of the porous membrane. When the inorganic particle layer is disposed on both sides of the porous membrane, the thicknesses of the inorganic particle layers disposed on one side and the other side can be the same or different from each other.

[0067] In one embodiment, the binder of the inorganic particle layer can be used as long as it can connect and fix the inorganic particles to form a porous inorganic particle layer, and all binders known in the art can be used without limitation. Non-limiting examples of the binder include, but are not limited to, acrylic resins such as polymethylmethacrylate (PMMA), polybutylacrylate (PBA), and polyacrylonitrile (PAN), silane compounds such as (3-aminopropyl)triethoxysilane, (3-aminopropyl)trimethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, and polymers thereof, styrene butadiene rubber (SBR), carboxyl methyl cellulose (CMC), polyvinylpyrrolidone (PVP), and polyvinylacetate (PVAc).

[0068] The inorganic particle layer can be prepared by the conventional preparation method that the inorganic particle layer is arranged on the porous film as known in the art. For example, water can be added to the mixture of the inorganic particles and the adhesive and stirred to make an inorganic particle layer slurry, then by any one of slot die coating, roll coating, spin coating, dip coating, bar coating, die coating, slit coating and inkjet printing or a combination thereof, the obtained inorganic particle layer slurry is coated on one or both sides of the porous film, thereby forming an inorganic particle layer on the porous film.

[0069] [Flexible polymer layer]

[0070] As an embodiment, the polymer forming the flexible polymer layer can be used without limitation as long as it is flexible and has lithium conductivity. The "flexible" may have the opposite meaning of "non-flexible" or "rigid". Furthermore, "flexible" may mean having flexibility when not provided on a porous substrate.

[0071] As an embodiment, the flexible polymer layer can be used without restriction as long as it is a polymer capable of conducting lithium ions and a polymer having elasticity. The flexible polymer layer can be composed of a cross-linked polymer capable of conducting lithium ions. For example, the flexible polymer layer can include a cross-linked copolymer, and the cross-linked copolymer includes a unit derived from a (meth) acrylic acid-based monomer and a unit derived from an ethylenically unsaturated multifunctional monomer.

[0072] As an embodiment, the (meth)acrylic acid-based monomer can play a role in the dissociation and transport of lithium salts, thereby improving the ionic conductivity of the flexible polymer layer.

[0073] As an embodiment, the (meth)acrylic acid-based monomer may include, for example, one or more of the (meth)acrylic acid esters consisting of methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, allyl (meth)acrylate, 2-methylpropyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, benzyl (meth)acrylate, hydroxyphenyl (meth)acrylate, and methoxyphenyl (meth)acrylate; or methacrylic acid, vinylacetic acid, crotonic acid, isocrotonic acid, pentenoic acid, allylacetic acid, maleic acid, fumaric acid, tiglic acid, angelic acid, citraconic acid, and mesaconic acid. One or more of (meth)acrylic acids such as acrylates and acrylates may be used, but the invention is not limited thereto.

[0074] As an embodiment, the ethylenically unsaturated multifunctional monomer may be a multifunctional acrylate-based monomer. When the ethylenically unsaturated multifunctional monomer is a multifunctional acrylate monomer, it can play a more excellent role in the dissociation and transmission of lithium salts, thereby improving the ionic conductivity of the flexible polymer layer, and therefore it may be more preferred.

[0075] As an embodiment, the ethylenically unsaturated multifunctional monomer may include, for example, one or more of 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, pentaethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyether polyol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol pentaacrylate, but is not limited thereto.

[0076] As an embodiment, by crosslinking the (meth) acrylic monomer and the ethylenically unsaturated multifunctional monomer in an appropriate ratio, the elasticity of the flexible polymer layer can be further improved. In the specific embodiment, relative to the content of total monomers, the composition ratio of the ethylenically unsaturated multifunctional monomer in the crosslinked copolymer can be 0.1-50 mol%, but as long as a flexible crosslinked polymer is provided, there is no particular restriction. For example, the composition ratio can be more than 0.1 mol%, more than 0.5 mol%, more than 1 mol%, more than 5 mol%, less than 50 mol%, less than 40 mol%, less than 30 mol%, less than 20 mol%, less than 10 mol%, and can be any value therebetween. For example, the composition ratio can be 0.1-50 mol%, 1-40 mol%, 1-30 mol%, 1-20 mol%, 1-10 mol%.

[0077] As an embodiment, the flexible polymer layer may include a polymer formed by reacting the (meth) acrylic acid-based monomer and the ethylenically unsaturated multifunctional monomer in a weight ratio of 90 to 99: 1 to 10, and is not limited thereto. For example, the weight ratio may be 90 to 99: 1 to 10, 91 to 99: 1 to 9, 92 to 99: 1 to 8, 93 to 99: 1 to 7, 94 to 99: 1 to 6, 95 to 99: 1 to 5, and is not limited thereto.

[0078] As an embodiment, in order to further improve the elasticity and ionic conductivity of the flexible polymer layer, the following additives may be selectively further included, but are not limited thereto.

[0079] As an additive to the flexible polymer layer, a lithium salt may be selectively further included. After the functional groups of the (meth) acrylic acid monomer and the ethylenically unsaturated multifunctional monomer are dissociated, the anions of the lithium salt act as nucleophiles, further improving the crosslinking degree of the crosslinked copolymer, thereby further improving the elasticity and other mechanical properties of the flexible polymer layer.

[0080] As an embodiment, the lithium salt can be used without restriction as long as it is a lithium salt known in the technical field, but for example, LiPF6, LiTFSI, LiFSI, LiBF4, LiAsF6, LiBOB, LiDFOB, LiClO4, LiNO3, LiBETI, LiCTFSI, LiB(CN)4, etc. can be used.

[0081] As an embodiment, based on the total weight of the flexible polymer layer, the content of the lithium salt may be 40 wt % or less, 35 wt % or less, 30 wt % or less, 25 wt % or less, 20 wt % or less, 0.1 wt % or more, 0.5 wt % or more, 1 wt % or more, or a value in between. For example, the content of the lithium salt may be 0.1-35 wt %, 0.5-30 wt %, or 1-20 wt %, but is not limited thereto.

[0082] In addition, when forming the flexible polymer layer, in addition to the monomer, a free radical additive may be selectively further included as an additive. The free radical additive may assist the initiator, thereby helping the cross-linking reaction to proceed uniformly even under conditions including factors that interfere with the cross-linking reaction, thereby further improving the elasticity and other mechanical properties of the flexible polymer layer.

[0083] Although not limited, examples of the free radical additive may further include one or more of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), 4-oxo-2,2,6,6-tetramethyl-1-peperidine 1-oxyl (oxoTEMPO), and di-t-butylnitroxide (DNTBNO).

[0084] As an embodiment, based on the total weight of the flexible polymer layer, the content of the free radical additive can be 5% by weight or less, 1% by weight or less, 0.5% by weight or less, 0.1% by weight or more, 0.5% by weight or more, 1% by weight or more, or a value between the above values, for example, 0.1-5% by weight, but not limited thereto. Alternatively, 30-60% by weight, 40-50% by weight of the free radical additive can be used relative to the amount of the initiator added, but not limited thereto.

[0085] In addition, when forming the flexible polymer layer, a highly reactive additive may be selectively further included. The highly reactive additive may further improve the mechanical and physical properties of the flexible polymer layer such as strength by increasing the hydrogen bonding force of the cross-linked copolymer, and may further increase the cross-linking degree of the cross-linked copolymer.

[0086] As an embodiment, the highly reactive additive may further include one or more of carboxylic anhydrides, amines, imines and thiols.

[0087] As an embodiment, as examples of the carboxylic anhydride, maleic anhydride, fumaric anhydride, etc. can be cited, but it is not limited to this. As examples of the amines, poly(N-hydroxyethyl acrylamide) (PHEAA), poly(N-isopropylacrylamide) (PNIPAM), etc. can be cited, but it is not limited to this. As examples of the imines, polyethyleneimine (PEI) can be cited, but it is not limited to this. The thiol can be a compound containing a thiol group at the end. As examples of the thiol, 2-ethylhexyl 3-mercaptopropionate, pentaerythritol tetrakis (3-mercaptopropionate) can be cited, but it is not limited to this.

[0088] As an embodiment, based on the total weight of the flexible polymer layer, the content of the highly reactive additive may be 5 wt % or less, 4 wt % or less, 3 wt % or less, 2 wt % or less, 0.1 wt % or more, 0.5 wt % or more, 1 wt % or more, or a value in between. For example, the content of the highly reactive additive may be 0.1-5 wt %, 0.5-4 wt %, or 1-3 wt %, but is not limited thereto.

[0089] In order to realize a high-capacity battery, it is advantageous to thin the diaphragm. From the viewpoint that the capacity of the battery can be further increased by thinning the diaphragm, while the desired dendrite growth of the present invention can be suppressed and the elasticity and ion conductivity of the diaphragm can be fully improved, when the thickness of the porous substrate is set to A and the thickness of the flexible polymer layer is set to B, B / A can be more than 0, less than 1.0, less than 0.9, less than 0.8, less than 0.7, less than 0.66, less than 0.6, less than 0.5, less than 0.4, more than 0.05, more than 0.1, more than 0.15, more than 0.2, more than 0.22, and can be any value between the above values. For example, the B / A can be 0.1 to 1.0, 0.15 to 0.8, 0.2 to 0.7, 0.2 to 0.6, and is not limited thereto. When the flexible polymer layer is formed on only one side of the porous substrate, the thickness B of the flexible polymer layer refers to the thickness of one side. When the flexible polymer layer is formed on both sides of the porous substrate, the thickness B of the flexible polymer layer refers to the sum of the thicknesses formed on both sides.

[0090] As an embodiment, the flexible polymer layer may be formed on one or both sides of the porous substrate, in which case the thickness of the flexible polymer layer on each side may be greater than 0 μm, greater than 0.1 μm, greater than 0.5 μm, greater than 1 μm, greater than 2 μm, greater than 3 μm, less than 5 μm, less than 4 μm, and may be any value between the above values. For example, the thickness of the flexible polymer layer on each side may be 0.1-5 μm, 0.1-4 μm, 0.1-3 μm, or 0.1-2 μm.

[0091] [Hybrid Diaphragm]

[0092] The hybrid separator according to one embodiment of the present invention may include the porous substrate and a flexible polymer layer, wherein the flexible polymer layer is disposed on at least one side of the porous substrate and is capable of conducting lithium ions, and the lithium ion conductivity of the hybrid separator at 25° C. may be 10 -4 S / cm or more, 10 -3 S / cm or more, 10 -2 S / cm or less, and can be any value between the above values. For example, a -4 -10 -2 S / cm, 10 -3 -10 -2 S / cm, 4.0×10 -3 -10 -2 S / cm or 4.0×10 -3 -7.0×10 -3 A hybrid separator having excellent lithium ion conductivity of 2000 S / cm and a lithium secondary battery including the hybrid separator.

[0093] The hybrid separator according to one embodiment of the present invention may have a lithium ion conductivity that satisfies the above range even if it includes a flexible polymer layer, and by providing the flexible polymer layer as the outermost layer, the formation of lithium dendrites may be suppressed. More specifically, the lithium ion conductivity of the hybrid separator at 25° C. may be calculated by dividing the thickness value of the separator after impregnation with a carbonate liquid electrolyte by the product of the impedance value measured between stainless steel electrodes and the separator area.

[0094] In addition, the flexible polymer layer has elasticity, so it can play the role of reinforcing material, and has the advantage of improving the mechanical properties of the entire diaphragm. In addition, the flexible polymer layer has excellent ionic conductivity, so that it can play a role similar to that of a liquid electrolyte. In addition, even if the liquid electrolyte is lost, the flexible polymer layer will act like a solid electrolyte, so that the migration of lithium can be carried out smoothly, so the life of the battery can be extended, and a stable battery in terms of fire can be provided. In addition, compared with the liquid electrolyte, the flexible polymer layer has low reactivity with lithium, so the increase in resistance caused by the depletion of the liquid electrolyte can be suppressed, and it can help to improve the battery life characteristics. In addition, the volume change of the battery is suppressed by alleviating the thickness change during the charge / discharge of the battery, so the stability of the battery can be improved.

[0095] When the flexible polymer layer is formed on the electrode of the negative electrode or the positive electrode, even if the electrode and the separator are integrated, a gap space may appear between the electrode and the separator during the electrode assembly process, and lithium dendrites may be formed in this portion. However, a hybrid separator according to an embodiment of the present invention is formed by integrating with a flexible polymer layer on a porous substrate, so it can be formed in a tightly adhered manner without a gap. Alternatively, a portion of the flexible polymer layer can be integrated by immersing into the pores from the surface of the porous substrate. Therefore, no gap is generated during the electrode assembly process, and the generation of lithium dendrites can be further suppressed.

[0096] A first embodiment of a hybrid separator according to one embodiment of the present invention may be a polyolefin-based porous film and a flexible polymer layer capable of conducting lithium ions stacked on one side of the polyolefin-based porous film.

[0097] A second embodiment may be a polyolefin-based porous film and flexible polymer layers capable of conducting lithium ions stacked on both surfaces of the polyolefin-based porous film.

[0098] A third embodiment may be a composite film having an inorganic particle layer in which inorganic particles are connected to form pores on one side of a polyolefin-based porous film, and a flexible polymer layer capable of conducting lithium ions is stacked on one side of the composite film.

[0099] A fourth embodiment may be a composite film having an inorganic particle layer in which inorganic particles are connected to form pores on one side of a polyolefin-based porous film, and flexible polymer layers capable of conducting lithium ions are stacked on both sides of the composite film.

[0100] A fifth embodiment may be a composite film having inorganic particle layers in which inorganic particles are connected to each other to form pores on both sides of a polyolefin-based porous film, and a flexible polymer layer capable of conducting lithium ions is laminated on one side of the composite film.

[0101] The sixth embodiment may be a composite film having an inorganic particle layer in which inorganic particles are connected to each other to form pores on both sides of a polyolefin-based porous film, and a flexible polymer layer capable of conducting lithium ions is laminated on both sides of the composite film.

[0102] The first to sixth embodiments are explanations of a specific embodiment of the present invention and are not limited thereto. In addition, other layers may be provided between the layers without limitation. In addition, in the third to sixth embodiments, the inorganic particle layer and the flexible polymer layer may be formed by stacking two or more layers.

[0103] In addition, as an embodiment, from the viewpoint of making the porous substrate and the flexible polymer layer adhere better and more tightly, in the case of using the composite membrane with the inorganic particle layer, after coating the slurry for forming the inorganic particle layer on the porous membrane, a flexible cross-linked polymer coating solution is coated on the slurry coating without undergoing a drying process or undergoing partial drying (for example, drying to a solvent content of less than 30%), so that the interface between the inorganic particle layer and the flexible polymer layer can be mixed and form a more solid coating.

[0104] In addition, the flexible polymer layer can be impregnated into and fill at least a portion of the pores of the porous substrate, and the interface is better and more tightly adhered, so that no slip occurs when assembling the battery, and the formation of lithium dendrites can be suppressed during the charge and discharge process, and the ion conductivity can be further improved.

[0105] Alternatively, a slurry for forming an inorganic particle layer may be coated on the porous membrane, and then the flexible cross-linked polymer coating solution may be coated after a drying process.

[0106] As an embodiment, the total thickness of the hybrid membrane can be 50 μm or less, 40 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 3 μm or more, 5 μm or more, 10 μm or more, 11 μm or more, or a value between the above values. For example, the total thickness of the hybrid membrane can be 3-50 μm, 5-50 μm, 8-40 μm, 10-30 μm, or 11-15 μm, but is not limited thereto.

[0107] As an embodiment, the porosity of the hybrid separator is not limited, but for example, the porosity may be 40% or less, 30% or less, 25% or less, 20% or less, 5% or more, 10% or more, 13% or more, 15% or more, 16% or more, 17% or more, 18% or more, 19% or more, and may be any value between the above values. For example, the porosity may be 5-30%, 10-25%, 10-20%, 13-20%, 15-20%, and is not limited thereto. Even in the case where the porosity is 20% or less, by using a flexible polymer layer that allows lithium migration, a very excellent lithium ion conductivity can be provided compared to a separator having the same level of porosity without using the flexible polymer layer.

[0108] Since the flexible polymer layer as described above is formed in the hybrid separator according to one embodiment of the present invention, the porosity of the hybrid separator may be reduced compared to the original porosity of the porous substrate. However, despite the reduced porosity, the hybrid separator has a porous structure that can satisfy the lithium ion conductivity of 10 -4 -10 -2 The effect of S / cm on physical properties.

[0109] As an embodiment, the thermal shrinkage of the hybrid diaphragm of the composite membrane having an inorganic particle layer on one or both sides of the porous substrate and a polyolefin-based porous membrane at 150°C can be 30% or less, 25% or less, 20% or less, 15% or less, 5% or less, 4% or less, or 3% or less. Although the lower limit of the thermal shrinkage is not limited, it can be more than 0.1%, more than 1%, and can be any range between the values ​​recorded above. For example, the thermal shrinkage can be 1-30%, 1-25%, 1-20%, 1-10%, 1-5%, 1-3%, 2-25%, 2-20%, 2-10%, 2-5%, 2-3%, 5-25%, and is not limited thereto. The thermal shrinkage can be different according to the type of porous substrate, and a lower thermal shrinkage can be provided in the case of a composite membrane having an inorganic particle layer on one or both sides of a polyolefin-based porous membrane compared to the case of a polyolefin-based porous membrane. For example, when the porous substrate is a polyolefin-based porous film, the heat shrinkage rate may be 1-30%, 5-25%, 10-20% or 10-15%, and when the porous substrate is a composite film, the heat shrinkage rate may be 1-5%, 1-3%, 2-3%. In the case of a film formed only of the polymer used in the flexible polymer layer of the present invention, the heat shrinkage rate may be 50% to 90% or more, but the porous substrate in the hybrid separator according to one embodiment of the present invention prevents the thermal shrinkage of the flexible polymer layer, so that the physical property of the hybrid separator having a heat shrinkage rate of 30% or less can be finally achieved.

[0110] As an embodiment, the needle puncture strength of the hybrid separator according to ASTM D3763_02 may be 2.5N or more, 3N or more, 3.5N or more, 3.9N or more, 4.0N or more, 8N or less, 7N or less, 6N or less, 5N or less, 4.5N or less, and may be any value between the above values. For example, the needle puncture strength may be 2.5-8N, 3-8N, 3.5-8N, 3.9-8N, 3.9-4N, and is not limited thereto.

[0111] In addition, the tensile strength of the hybrid membrane according to ASTM D882 may be 80 MPa or more, 100 MPa or more, 130 MPa or more, 150 MPa or more, 180 MPa or more, 185 MPa or more, 220 MPa or less, 200 MPa or less, 190 MPa or less, and may be any value between the above values. For example, the tensile strength may be 80-220 MPa, 90-210 MPa, 100-200 MPa, 130-185 MPa, or 180-185 MPa, and is not limited thereto.

[0112] As an embodiment, the elongation at break of the hybrid separator at 25°C may be more than 0%, more than 10%, more than 20%, more than 30%, more than 40%, more than 50%, more than 60%, less than 90%, less than 80%, less than 70%, or a value between the above values. For example, the elongation at break may be 20-90%, 30-80%, 50-80%, 60-70%, but is not limited thereto. The elongation at break may be measured according to ASTM D882.

[0113] As an embodiment, the elastic recovery rate of the diaphragm provided with the flexible polymer layer at 20% strain may be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100% or less, or a value between the above values, specifically 50-100%, 50-80%, but not limited thereto. The elastic recovery rate can be calculated by dividing the measured value of the length reduced after the external pressure is removed by the difference between the maximum length increased before the external pressure is removed and the original sample length.

[0114] As an embodiment, the hybrid membrane may satisfy all of the above physical property ranges, but is not limited thereto.

[0115] [Method for manufacturing hybrid diaphragm]

[0116] As long as a hybrid separator according to an embodiment of the present invention can be provided, the manufacturing method, conditions, etc. are not limited, but are described by way of example. If there are terms in the following content that have been described in the above content, the same description can be applied, so for convenience, the description is omitted.

[0117] As an embodiment, when the porous substrate is a polyolefin-based porous membrane as an example, it can be manufactured by a method including the following steps: coating a flexible cross-linked polymer coating solution containing an acrylic monomer, an ethylenically unsaturated multifunctional monomer and an initiator on one side or both sides of the polyolefin-based porous membrane, and performing thermal curing or photocuring such as ultraviolet (UV) curing to form a flexible polymer layer.

[0118] As one embodiment, when the porous substrate is a polyolefin-based porous film having an inorganic particle layer formed on one or both sides thereof, it can be manufactured by two embodiments.

[0119] That is, the first embodiment can be manufactured by a method comprising the following steps: coating a slurry for forming an inorganic particle layer on one or both sides of a polyolefin-based porous film, and then drying to form an inorganic particle layer; coating a flexible cross-linked polymer coating solution containing an acrylic monomer, an ethylenically unsaturated multifunctional monomer, and an initiator on one or both sides of a composite film formed with the inorganic particle layer, and performing thermal curing or UV curing to form a flexible polymer layer. At this time, the flexible polymer layer can be formed on the inorganic particle layer.

[0120] The second embodiment is that it can be manufactured by a method comprising the following steps: when manufacturing a composite membrane having an inorganic particle layer on one or both sides of a polyolefin-based porous membrane, a slurry for forming an inorganic particle layer is coated on at least one side of the polyolefin-based porous membrane, and then before drying the slurry coating, a flexible cross-linked polymer coating solution comprising an acrylic monomer, an ethylenically unsaturated multifunctional monomer and an initiator is coated on the upper surface of the slurry coating and dried, and then thermally cured or UV cured to form a flexible polymer layer.

[0121] In addition, as an embodiment, for the porous substrate, before the flexible cross-linked polymer coating solution or the slurry for forming the inorganic particle layer is coated on the polyolefin-based porous membrane, a step of subjecting the surface of the porous substrate to a corona discharge treatment or a plasma discharge treatment in the atmosphere to perform a hydrophilic treatment may be further included. As an example, a method of imparting hydrophilicity to the surface of the porous substrate may be to form a hydroxyl group, a carboxyl group or an aldehyde group on the surface of the porous substrate by corona discharge or plasma discharge treatment in an atmosphere of oxygen and ozone such as the atmosphere, but chemical treatment is not excluded.

[0122] As an embodiment, the method for preparing the flexible cross-linked polymer coating solution can be prepared by using all methods known in the art, and the method is not limited. However, according to a non-limiting example, it can be prepared by mixing an acrylic monomer, an ethylenically unsaturated multifunctional monomer, and an initiator without a separate solvent. Alternatively, it can be prepared by including a solvent.

[0123] The initiator may be any thermal polymerization initiator or UV curing initiator commonly used in the art. Examples of thermal polymerization initiators include azo compounds, organic peroxides, and hydrogen peroxide, but are not limited thereto.

[0124] As an embodiment, when the acrylic acid-based monomer and the ethylenically unsaturated multifunctional monomer are included in the flexible cross-linked polymer coating solution in an appropriate ratio and cross-linked, the elasticity of the prepared flexible polymer layer can be further improved. In the specific embodiment, the molar ratio of the acrylic acid-based monomer to the ethylenically unsaturated multifunctional monomer in the flexible cross-linked polymer coating solution can be, for example, 2 or more, 5 or more, 10 or more, 20 or more, 30 or more, 50 or more, 200 or less, 150 or less, 120 or less, 100 or less, or a value between the above values, and the molar ratio can be specifically 2 to 200, 5 to 150, 10 to 120, 20 to 100, 30 to 100, 50 to 100, 60 to 100, 70 to 100, 80 to 100, 90 to 100, but is not limited thereto.

[0125] For example, the flexible cross-linked polymer coating solution may include a monomer mixture of the acrylic acid-based monomer and the ethylenically unsaturated multifunctional monomer in a weight ratio of 90 to 99:1 to 10 and an initiator, and the content of the initiator may be 0.1-5 wt %, and is not limited thereto.

[0126] In order to provide a flexible polymer layer with further improved elasticity and ionic conductivity, according to a specific embodiment, the flexible cross-linked polymer coating solution may further selectively include the following additives, but is not limited thereto. The same explanation as the above explanation can be applied to the reasons for adding the additives and the types of the additives, so for convenience, the explanation is omitted.

[0127] As an embodiment, the flexible cross-linked polymer coating solution may selectively further comprise a lithium salt. Based on the total solid weight of the flexible cross-linked polymer coating solution, the content of the lithium salt may be less than 30 wt%, less than 25 wt%, less than 20 wt%, more than 0.1 wt%, more than 0.5 wt%, more than 1 wt%, or a value between the above values, specifically 0.1-30 wt%, 0.5-25 wt%, or 1-20 wt%, but is not limited thereto.

[0128] As an embodiment, the flexible cross-linked polymer coating solution may selectively further include a free radical additive, for example, it may further include one or more of a free radical additive group consisting of (2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO), 4-oxo-2,2,6,6-tetramethyl-1-piperidin-1-oxy (oxoTEMPO) and di-tert-butylnitroxide (DNTBNO).

[0129] As an embodiment, based on the total solid weight of the flexible cross-linked polymer coating solution, the content of the free radical additive can be less than 30 weight %, less than 25 weight %, less than 20 weight %, more than 0.1 weight %, more than 0.5 weight %, more than 1 weight %, or a value between the above values, specifically 0.1-30 weight %, 0.5-25 weight % or 1-20 weight %, but is not limited thereto.

[0130] As an embodiment, the flexible cross-linked polymer coating solution may selectively further include a highly reactive additive, and more specifically, may further include one or more of carboxylic anhydrides, amines, imines, and thiols.

[0131] As an embodiment, based on the total solid weight of the flexible cross-linked polymer coating solution, the content of the highly reactive additive may be 30 wt % or less, 25 wt % or less, 20 wt % or less, 0.1 wt % or more, 0.5 wt % or more, 1 wt % or more, or values ​​in between. For example, the content of the highly reactive additive may be 0.1-30 wt %, 0.5-25 wt %, or 1-20 wt %, but is not limited thereto.

[0132] As an embodiment, the slurry for forming the inorganic particle layer may be prepared by any method known in the art without limitation.

[0133] As an embodiment, as non-limiting examples of coating processes, one or a combination of slot extrusion coating, roller coating, spin coating, dip coating, rod coating, die coating, slot coating and inkjet printing may be used.

[0134] As an embodiment, the process of forming the flexible polymer layer may be heating after coating the composition to perform drying and cross-linking reactions. As a specific embodiment for more smoothly performing drying and cross-linking reactions, the heating temperature may be above 40°C, above 50°C, above 60°C, above 65°C, below 150°C, below 120°C, below 100°C, below 90°C, below 80°C, or a value between the above values. For example, the heating temperature may be 40-150°C, 50-120°C, 60-100°C, 60-90°C, or 65-80°C, but is not limited thereto.

[0135] As an embodiment, the heating time for more smoothly performing the drying and cross-linking reaction can be 1 minute or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 3 hours or less, 2 hours or less, 1 hour or less, or a value between the above values. For example, the heating time can be 1 minute to 3 hours, 5 minutes to 3 hours, 30 minutes to 3 hours, 20 minutes to 2 hours, or 30 minutes to 1 hour, but is not limited thereto.

[0136] As an embodiment, the heating atmosphere is not limited, but may be, for example, an atmospheric atmosphere or preferably may be an atmosphere free of moisture and oxygen.

[0137] As an embodiment, the method for arranging the inorganic particle layer on the porous membrane is not limited as long as it is prepared by a conventional preparation method. As a non-limiting example, water can be added to the mixture of inorganic particles and adhesive and stirred to prepare an inorganic particle layer slurry, or a slurry mixed with inorganic particles and water can be prepared and used without an adhesive. By slit extrusion coating, roller coating, spin coating, dip coating, rod coating, die coating, slit coating and inkjet printing, one or a combination of them, the obtained inorganic particle layer slurry is coated on one or both sides of the porous membrane, so that the inorganic particle layer can be arranged on at least one side of the porous membrane.

[0138] As an embodiment, a lithium battery including a separator of one embodiment described above may be provided, and the lithium battery may refer to all electrochemical devices containing lithium, and the type thereof is not particularly limited. As a non-limiting example of a lithium battery, a lithium secondary battery may be cited. The lithium secondary battery is well known, and its composition is also known, so it is not specifically described in the present invention.

[0139] As an embodiment, the lithium battery may include: a positive electrode; a negative electrode; and the mixed separator of this specific embodiment between the positive electrode and the negative electrode. At this time, the positive electrode and the negative electrode may be any positive electrode and negative electrode that are generally used in lithium secondary batteries without limitation.

[0140] The embodiments of the present invention are further described below with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are only used to illustrate the present invention and are not used to limit the claims. Various modifications and variations can be made to the embodiments within the scope of the present invention and the technical concept, which is obvious to those skilled in the art, and it is natural that such modifications and variations belong to the scope of the claims.

[0141] The physical properties were measured as follows.

[0142] <Ionic conductivity>

[0143] The ion conductivity of the hybrid membrane of each example and comparative example was calculated by the following mathematical formula.

[0144] Ionic conductivity = L ÷ (R × A)

[0145] Where, L = thickness of the hybrid separator impregnated with liquid electrolyte (unit: cm)

[0146] R = Impedance value of the hybrid separator immersed in liquid electrolyte at 25°C (unit: Ω = 1 / S) (real value when the imaginary part of the impedance value is 0)

[0147] A = The area of ​​overlap between the two electrodes when measuring impedance (cm 2 )

[0148] To determine the R value, the hybrid separator was punched into concentric circles with a diameter of 18 mm and then immersed in a carbonate liquid electrolyte (1M LiPF6 in 3:5:2 (v / v / v) EC / EMC / DEC) for 1 hour. At this time, the L value was measured using a Mitutoyo micrometer and the A value was determined to be 2.5447 cm 2 . After that, a 2032 standard coin cell (SUS material) was assembled with a separator impregnated with a liquid electrolyte, and the constant voltage impedance value was measured using the IM6 equipment of Zahner Company in the range of 100MHz to 100mHz, with an initial voltage of 0V and an amplitude of 5mV. The real impedance value R when the imaginary part value is 0 is obtained by equivalent circuit fitting of the measured impedance value.

[0149] <Porosity>

[0150] The porosity of the separator is calculated by cutting a rectangular sample of A cm × B cm using the following mathematical formula. A / B are cut into 5-20 cm ranges and measured.

[0151] Porosity = {(A×B×T)-(M÷ρ)÷(A×B×T)}×100

[0152] Where, T = thickness of the diaphragm (cm)

[0153] M = weight of sample (g)

[0154] ρ = true density of the entire diaphragm (g / cm 3 )

[0155] <Heat shrinkage>

[0156] Cut the diaphragm into a square shape with a side length of 10 cm to prepare the sample, and then use a camera to measure and record the area of ​​the sample before the experiment. Place five pieces of paper above and below the sample so that the sample is located in the center, and fix the four sides of the paper with clips. Place the paper-wrapped sample in a hot air circulation dryer at 150°C for 1 hour. After the placement is completed, take out the sample, use a camera to measure the length change of the diaphragm in the MD direction and TD direction respectively, and calculate the shrinkage rate by the following mathematical formula. Calculate the values ​​in the MD direction and TD direction respectively, and record the average value.

[0157] Shrinkage rate (%) = (side length of the sample before heating (L0) - side length of the deformed sample after heating (L)) ÷ side length of the sample before heating (L0) × 100

[0158] <Needle Puncture Strength>

[0159] The needle puncture strength of the separator was measured according to ASTM D3763_02.

[0160] <Tensile Strength and Elongation at Break>

[0161] The tensile strength and elongation at break of the separator were measured according to ASTM D882 at 25° C. The values ​​in the MD direction and the TD direction were calculated respectively, and the average values ​​were recorded.

[0162] <Elastic recovery rate>

[0163] The elastic recovery value of the separator is calculated by the integrated area change rate of the curve obtained after a tensile test using a universal testing machine.

[0164] Elastic recovery rate (%) = (Y) ÷ (X) × 100

[0165] X = the integrated area of ​​the stress-strain curve obtained when a tensile force is applied to the specimen

[0166] Y = integrated area of ​​the stress-strain curve obtained when the tensile force is removed

[0167] In order to determine the X value and the Y value, a sample with a size of 60 mm × 10 mm (length × width, respectively) was prepared. The sample was clamped so that the distance L0 between the universal testing machine fixtures was 40 mm, and the sample was stretched at a speed of 100 mm / min so that the final length L was 48 mm, and a stress-strain curve for determining the X value was obtained, and then the external force was removed so that it could immediately return to its original length, thereby obtaining a stress-strain curve for determining the Y value. The elastic recovery rate value was calculated from the obtained X value and Y value.

[0168] <Thickness>

[0169] For the thickness of the diaphragm, a contact thickness gauge having a thickness accuracy of 0.1 μm was used.

[0170] <Gerlai air permeability>

[0171] The Gurley air permeability of the porous substrate was measured using a Densometer manufactured by Toyoseiki Co., Ltd. in accordance with ASTM D726. The time required for 100 cc of air to pass through an area of ​​1 square inch of the porous substrate was recorded in seconds and compared.

[0172] <Whether lithium dendrites are generated in the battery>

[0173] In Li(Ni 0.8 Co 0.1 Mn 0.1 ) The separator manufactured in the embodiment and the comparative example is set between the O2 positive electrode and the graphite negative electrode to assemble a single-plate battery. A liquid electrolyte of 1.15M LiPF6 and 5 wt% fluoroethylene carbonate (Fluoroethylene Carbonate, FEC) dissolved in a mixed solvent of ethylene carbonate (ethylene carbonate, EC) / ethyl methyl carbonate (ethyl methyl carbonate, EMC) / diethyl carbonate (diethyl carbonate, DEC) (3:5:2, v / v / v) is injected into the battery. For the battery, CC / CV mode charging and CC mode discharging are repeated 100 times at a current density of 0.5C in the voltage range of 3.0V to 4.2V, and then disassembled in the charged state to confirm whether lithium dendrites are generated and grown. The negative electrode is recovered from the disassembled battery in an environment not exposed to oxygen and moisture, and the residual lithium salt is washed with a mixed solvent of EC / EMC / DEC and then dried. The surface of the dried negative electrode is observed by visual inspection and SEM, and the presence of lithium dendrites in the battery is confirmed.

[0174] <Molecular weight>

[0175] The weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene-equivalent molecular weights determined by gel permeation chromatography (GPC) which measures molecular weight using commercially available monodisperse polystyrene polymers (standard samples) having different polymerization degrees as standard materials.

[0176] [Preparation Example 1] Preparation of Inorganic Particle Layer Using Water-Based Slurry

[0177] 1.0 part by weight of a carboxylic acid polymer-based inorganic dispersant (BASF, Dispex ® AA 4030), then 100 parts by weight of boehmite (γ-AlO(OH)) with an average particle size of 500 nm was added and stirred, and dispersed using a bead mill to prepare a uniform water-based slurry base solution. 10% acrylic acid-based polymer (Sigma-Aldrich, CAS No.: 9003-05-8, M 4030) was added to the prepared base solution relative to 50 parts by weight of the boehmite addition. n : 150000) aqueous solution, and further add 40 parts by weight of distilled water to dilute it to a viscosity suitable for the target coating thickness, and then stir it. Before coating, add 1000ppm of wetting additive (BASF, TEXAPON ® SB 3 UNKONS), followed by further stirring for 1 hour, thereby preparing a water-based slurry for an inorganic particle layer.

[0178] [Preparation Example 2] Preparation of Flexible Cross-linked Polymer Coating Solution (1)

[0179] 95 wt % of butyl methacrylate, 4 wt % of poly(ethylene glycol) dimethacrylate having a number average molecular weight (Mn) of 550 g / mol, and 1 wt % of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to prepare a flexible cross-linked polymer coating solution. The prepared solution was stored in a refrigerated environment below 5° C. and consumed by coating and cross-linking reactions within 2 hours of preparation.

[0180] [Preparation Example 3] Preparation of Flexible Cross-linked Polymer Coating Solution (2)

[0181] 95 wt% of butyl methacrylate, 4 wt% of poly(ethylene glycol) dimethacrylate having an Mn of 550 g / mol, and 1 wt% of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to prepare a base solution of a flexible cross-linked polymer coating solution. Thereafter, 20 wt% (20 mol% relative to the amount of butyl methacrylate added) of a lithium salt of lithium bis(fluorosulfonyl)imide and lithium difluoro(oxalate)borate in a weight ratio of 8:2 was mixed relative to the total weight of the polymer to prepare a flexible cross-linked polymer coating solution. The prepared solution was stored in a refrigerated environment below 5°C and consumed by coating and cross-linking reactions within 2 hours of preparation.

[0182] [Preparation Example 4] Preparation of Flexible Cross-linked Polymer Coating Solution (3)

[0183] 95 wt% of butyl methacrylate, 4 wt% of poly(ethylene glycol) dimethacrylate having an Mn of 550 g / mol, and 1 wt% of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to prepare a base solution of a flexible cross-linked polymer coating solution. Thereafter, 50 wt% of (2,2,6,6-tetramethylpiperidin-1-yl)oxy as a free radical additive relative to the amount of the initiator added was mixed to prepare a flexible cross-linked polymer coating solution. The prepared solution was stored in a refrigerated environment below 5°C and consumed by coating and cross-linking reactions within 2 hours of preparation.

[0184] [Preparation Example 5] Preparation of Flexible Cross-linked Polymer Coating Solution (4)

[0185] 95 wt% of butyl methacrylate, 4 wt% of poly(ethylene glycol) dimethacrylate having an Mn of 550 g / mol, and 1 wt% of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to prepare a base solution of a flexible cross-linked polymer coating solution. Thereafter, 3 wt% of maleic anhydride as a highly reactive additive relative to the cross-linked polymer coating solution base was mixed to prepare a flexible cross-linked polymer coating solution. The prepared solution was stored in a refrigerated environment below 5°C and consumed by coating and cross-linking reactions within 2 hours of preparation.

[0186] [Example 1] Production of hybrid diaphragm (1)

[0187] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0188] The flexible cross-linked polymer coating solution prepared in Preparation Example 2 was coated on both sides of the porous substrate by a bar coating method, and then hot-air dried and exposed to a metal halide lamp in a UV cross-linking device (wherein the oxygen concentration was adjusted to 500 ppm or less by nitrogen purge) to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm.

[0189] The total thickness of the prepared hybrid separator was 11 μm, and the physical properties were evaluated and shown in Table 1 below.

[0190] [Example 2] Production of hybrid diaphragm (2)

[0191] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0192] In order to coat the inorganic particle layer, both sides of the porous film were subjected to corona discharge treatment to introduce surface polar groups. At this time, the corona surface treatment was performed at a speed of 5 meters per minute (mpm).

[0193] The water-based slurry prepared in Preparation Example 1 was applied to both sides of the porous substrate and then dried to form an inorganic particle layer. The thickness of the inorganic particle layer formed on both sides after drying was 2 μm.

[0194] The flexible cross-linked polymer coating solution prepared in Preparation Example 2 was coated on the upper part of the inorganic particle layer on both sides, and then hot air dried and exposed to a metal halide lamp in a UV cross-linking device (wherein the oxygen concentration was adjusted to 500 ppm or less by nitrogen purge) to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm.

[0195] The total thickness of the prepared hybrid separator was 15 μm, and the physical properties were evaluated and shown in Table 1 below.

[0196] [Example 3] Production of hybrid diaphragm (3)

[0197] The manufacturing was performed by the same method as in Example 1, except that the thickness of each flexible polymer layer was adjusted to 3 μm in Example 1. The total thickness of the prepared hybrid separator was 15 μm, and the physical properties were evaluated and shown in Table 1 below.

[0198] [Example 4] Production of hybrid diaphragm (4)

[0199] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0200] The flexible cross-linked polymer coating solution prepared in Preparation Example 3 was coated on both sides of the porous substrate, followed by hot air drying and exposure to a metal halide lamp in a UV cross-linking device (wherein the oxygen concentration was adjusted to 500 ppm or less by nitrogen purge) to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm.

[0201] The total thickness of the prepared hybrid separator was 11 μm, and the physical properties were evaluated and shown in Table 1 below.

[0202] [Example 5] Production of hybrid diaphragm (5)

[0203] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0204] The flexible cross-linked polymer coating solution prepared in Preparation Example 4 was coated on both sides of the porous substrate, then dried with hot air, and exposed to a metal halide lamp in a UV cross-linking device (wherein the oxygen concentration was adjusted to 500 ppm or less by nitrogen purge) to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm.

[0205] The total thickness of the prepared hybrid separator was 11 μm, and the physical properties were evaluated and shown in Table 1 below.

[0206] [Example 6] Production of hybrid diaphragm (6)

[0207] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0208] The flexible cross-linked polymer coating solution prepared in Preparation Example 5 was coated on both sides of the porous substrate, followed by hot air drying and exposure to a metal halide lamp in a UV cross-linking device (wherein the oxygen concentration was adjusted to 500 ppm or less by nitrogen purge) to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm.

[0209] The total thickness of the prepared hybrid separator was 11 μm, and the physical properties were evaluated and shown in Table 1 below.

[0210] [Comparative Example 1]

[0211] The flexible cross-linked polymer coating solution of Preparation Example 2 was coated on a Teflon sheet and cured to prepare a flexible polymer sheet with a thickness of 19 μm.

[0212] The physical properties of the flexible polymer sheet prepared as described above were evaluated and are shown in Table 1 below.

[0213] [Comparative Example 2]

[0214] A separator was manufactured by the same method as in Example 2, except that the flexible polymer layer was not formed.

[0215] As the porous substrate, a polyethylene porous film having a thickness of 9 μm, a porosity of 45%, and a Gurley air permeability of 70 sec / 100 ml was used.

[0216] In order to coat the inorganic particle layer, both sides of the porous film were subjected to corona discharge treatment to introduce surface polar groups. At this time, the corona surface treatment was performed at a speed of 5 meters per minute (mpm).

[0217] The water-based slurry prepared in Preparation Example 1 was applied to both sides of the porous substrate and then dried to form an inorganic particle layer. The thickness of the inorganic particle layer formed on both sides after drying was 2 μm.

[0218] The total thickness of the prepared separator was 13 μm, and the physical properties were evaluated and shown in Table 1 below.

[0219] [Comparative Example 3]

[0220] The same method as in Example 1 was used except that the flexible polymer layer was repeatedly coated to produce a separator having a coating thickness of 5 μm on one side. The results are shown in Table 1.

[0221] [Table 1]

[0222]

[0223] As shown in Table 1 above, it was confirmed that in the embodiment, although the volume ratio of the pores serving as the migration path of lithium ions in the entire separator, i.e., the porosity, was less than 20%, the lithium ion conductivity was excellent at almost the same level as that of Comparative Example 2 which had no flexible polymer film and had a porosity as high as 45%.

[0224] At the same time, it was confirmed that it has excellent mechanical and physical properties, such as the elastic recovery rate for suppressing the growth of lithium dendrites inside the battery increased to more than 50%, and the needle puncture strength and tensile strength remained at similar or higher levels.

[0225] Furthermore, it was confirmed that when an inorganic particle layer was further included as in Example 2, the heat shrinkage rate was lower.

[0226] In addition, in the case where there is no polyolefin-based porous membrane and the flexible polymer sheet alone is included as in Comparative Example 1, it was confirmed that the thermal shrinkage rate is high, the ion conductivity is low, and the mechanical physical properties are poor.

[0227] Comparative Example 2 is a separator in a commonly used form, and is a case where inorganic particle layers are formed on both sides of a polyolefin-based porous film. However, it can be seen that in the embodiment of the present invention, although the porosity is lower than that of Comparative Example 2, there is no difference in lithium ion conductivity, and the conductivity is at the same level, while the physical properties are significantly improved in terms of elastic recovery rate.

[0228] Furthermore, as shown in Comparative Example 3, it is found that when B / A exceeds 1.0, the porosity and lithium ion conductivity are significantly reduced.

[0229] That is, it was confirmed that in Examples 1 to 6 according to one embodiment of the present invention, although the porosity was at a level of 20% or less, which was lower than the porosity of 45% of the original polyolefin-based porous membrane, the ion conductivity was at the same level as that of the existing separator in which the flexible polymer layer was not formed, such as Comparative Example 2. In addition, it was confirmed that the mechanical strength and elastic recovery rate were excellent. In addition, after assembling the battery and repeating charging and discharging 100 times, it was confirmed whether lithium dendrites were generated, and it was confirmed that the degree of lithium dendrite generation was significantly reduced compared with Comparative Example 2.

[0230] Furthermore, as shown in Example 2, it was confirmed that when the inorganic particle layer was formed on the porous substrate, the physical property of a heat shrinkage rate of 5% or less at 150° C. could be satisfied.

[0231] The above-described contents are merely examples of the application of the principles of the present invention, and other configurations may be included without departing from the scope of the present invention.

[0232] As described above, the present invention has been described through specific contents and limited embodiments, but this is only provided to help a more comprehensive understanding of the present invention. The present invention is not limited to the above embodiments, and technicians in the field of the present invention can make various modifications and variations through such descriptions.

[0233] Therefore, the idea of ​​the present invention should not be limited to the illustrated embodiments, and all contents of the claims and equivalents to the claims or equivalent modifications belong to the scope of the idea of ​​the present invention.

Claims

1. A lithium secondary battery, comprising a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a liquid electrolyte, The separator is a hybrid separator comprising a porous substrate and a flexible polymer layer, wherein the flexible polymer layer is disposed on at least one side of the porous substrate and is capable of conducting lithium ions. The lithium ion conductivity of the hybrid separator is 10 -4 -10 -2 S / cm.

2. The lithium secondary battery according to claim 1, wherein The porosity of the hybrid membrane is less than 40%.

3. The lithium secondary battery according to claim 1, wherein The hybrid separator has a heat shrinkage rate of 30% or less at 150°C.

4. The lithium secondary battery according to claim 1, wherein When the thickness of the porous substrate is defined as A and the thickness of the flexible polymer layer is defined as B, B / A is 1.0 or less.

5. The lithium secondary battery according to claim 4, wherein: The thickness of the flexible polymer layer on each side of the hybrid membrane is 0.1-5 μm.

6. The lithium secondary battery according to claim 1, wherein The porous substrate is a polyolefin-based porous film or a composite film having an inorganic particle layer on one or both sides of the polyolefin-based porous film.

7. The lithium secondary battery according to claim 1, wherein: The porous substrate has a thickness of 4-25 μm and a porosity of 30-70%.

8. The lithium secondary battery according to claim 1, wherein The flexible polymer layer is composed of a cross-linked polymer capable of conducting lithium ions.

9. The lithium secondary battery according to claim 8, wherein: The flexible polymer layer includes a cross-linked copolymer including units derived from an acrylic-based monomer and units derived from an ethylenically unsaturated multifunctional monomer.

10. The lithium secondary battery according to claim 8, wherein The flexible polymer layer further comprises any one or two or more additives selected from lithium salts, free radical additives and high-reactivity additives.

11. The lithium secondary battery according to claim 9, wherein The ethylenically unsaturated multifunctional monomer is a multifunctional acrylate-based monomer.

12. The lithium secondary battery according to claim 11, wherein The ethylenically unsaturated multifunctional monomer comprises one or more of 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, pentaethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polyether polyol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, di(trimethylolpropane) tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol pentaacrylate.

13. The lithium secondary battery according to claim 1, wherein The hybrid separator has a needle puncture strength of 3N or more according to ASTM D3763_02, and a tensile strength of 150-200 MPa according to ASTM D882.

14. The lithium secondary battery according to claim 1, wherein The hybrid diaphragm has an elongation at break of 20-90% at 25° C. and an elastic recovery rate of 50-100% at 20% strain.

15. A hybrid separator, comprising a porous substrate and a flexible polymer layer, wherein the flexible polymer layer is disposed on at least one side of the porous substrate and is capable of conducting lithium ions, The lithium ion conductivity of the hybrid separator is 10 -4 -10 -2 S / cm.

16. The hybrid membrane according to claim 15, wherein: The porous substrate is a polyolefin-based porous film or a composite film having an inorganic particle layer on one or both sides of the polyolefin-based porous film.

17. The hybrid membrane according to claim 15, wherein: The flexible polymer layer is composed of a cross-linked polymer capable of conducting lithium ions.

18. The hybrid membrane according to claim 17, wherein: The flexible polymer layer includes a cross-linked copolymer including units derived from an acrylic-based monomer and units derived from an ethylenically unsaturated multifunctional monomer.

19. The hybrid membrane according to claim 17, wherein: The flexible polymer layer further comprises any one or two or more additives selected from lithium salts, free radical additives and high-reactivity additives.

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