Hybrid separator and lithium secondary battery including the same

Abstract

To provide a hybrid separator and a lithium secondary battery including the hybrid separator.SOLUTION: According to an embodiment, a lithium secondary battery includes: a negative electrode; a positive electrode; a separator that is arranged to between the negative electrode and the positive electrode; and a liquid electrolyte. The separator is a hybrid separator including a porosity base material and a flexibility polymer layer that is arranged on at least one surface of the porosity base material and can perform a lithium ion conduction. A lithium ion conductive level of the hybrid separator is 10-4 to 10-2S / cm. The hybrid separator according to the present disclosure includes the flexibility polymer layer, and thus, realizes a good mechanical strength of the separator, and have an effect for surely reducing generation of a lithium dendrite in a charging and discharging step.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a hybrid separator and a lithium secondary battery including the same.

Background Art

[0002] Recently, lithium secondary batteries have been increased in capacity and size so as to be applicable to electric vehicles and the like. In order to exhibit a high capacity for the same volume, thinning is required, and ensuring the safety of the battery has become a very important factor.

[0003] A lithium secondary battery usually includes a separator disposed between a positive electrode and a negative electrode, and a polyolefin-based porous membrane is used as the separator. The polyolefin-based porous membrane has pores through which lithium ions can pass, but in the repeated charge / discharge process, it causes a bias phenomenon of lithium ions, forms lithium dendrites at the negative electrode, and the formed lithium dendrites can cause various problems in the battery.

[0004] Specifically, when lithium dendrites are formed, they grow into sharp needles. When the lithium dendrites grown in this way block the pores of the polyolefin-based porous membrane or pierce the polyolefin-based porous membrane, it may cause a short circuit inside the battery and cause stability problems such as a fire.

[0005] In addition, when the surface of newly grown lithium dendrites is exposed to the electrolyte, the electrolyte and lithium with a high specific surface area easily participate in an electrochemical side reaction, the electrolyte is easily depleted, and the life characteristics of the battery are deteriorated. Further, the change in the thickness of the electrode generated by the formation of lithium dendrites causes a change in the overall volume of the battery, thereby reducing the dimensional stability of the battery.

[0006] To solve such problems, various techniques for suppressing the growth of lithium dendrites have been proposed, but the development of technologies that can improve the mechanical properties and ionic conductivity of separators and solve all problems caused by lithium dendrites is not sufficient.

[0007] From another perspective, research has been conducted on all-solid-state batteries that use a solid-phase electrolyte between the positive electrode and the negative electrode. All-solid-state batteries necessarily require a solid electrolyte that transmits lithium ions. Solid electrolytes are roughly classified into organic (polymer) electrolytes and inorganic electrolytes. Since polymer electrolytes transmit lithium ions by hopping within the molecular chain, the phenomenon of lithium ion bias is reduced compared to the combination of liquid electrolytes and separators, lithium dendrites do not grow well, and they have excellent stability. However, in the case of polymers that do not contain liquids, the ionic conductivity at room temperature is extremely low, showing a level of about 10 -7 ~10 -4 S / cm. Also, most polymers are unstable at high voltages of 4 V or more and have the demerit of being brittle in mechanical strength. In order for polymer electrolytes to be commercialized, they need to be 50 μm or more thick. Therefore, it is very difficult for the mechanical strength of polymer electrolytes to reach the level equivalent to that of polyolefin-based porous substrates even after the battery thickness increases and through the crosslinking process. Also, for electric vehicle batteries and the like where thin-film materials are necessarily required to achieve high power and high capacity, it is actually difficult to apply them. Also, although it may vary depending on the type of polymer used, the thermal shrinkage rate of polymer electrolytes is larger than that of polyolefin-based porous substrates coated with ceramics, and the safety of the battery may be hindered.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to one aspect of the present disclosure, a hybrid separator including a flexible polymer layer capable of lithium ion conduction can be provided.

[0010] According to one aspect of the present disclosure, a novel concept hybrid separator including a flexible polymer layer capable of lithium ion conduction disposed on at least one surface of a porous substrate and a lithium secondary battery capable of suppressing the growth of lithium dendrites by including the same can be provided.

[0011] According to one aspect of the present disclosure, a novel concept hybrid separator that complements the demerits of a separator using a polyolefin-based porous substrate and the demerits of a polymer electrolyte can be provided.

[0012] According to one aspect of the present disclosure, a thin film separator can be provided while maintaining the ion conductivity and mechanical physical properties of the polyolefin-based porous substrate itself and without increasing the total thickness of the separator.

[0013] According to one aspect of the present disclosure, a hybrid separator capable of significantly suppressing the growth of lithium dendrites even in a repeated charge / discharge process can be provided.

[0014] According to one aspect of the present disclosure, although the total thickness of the separator is a thin film of 50 μm or less and the porosity is as low as 40% or less, at 25°C, the lithium ion conductivity is 10 -4 S / cm or more, 10 -3 S / cm or more, 10 -2 S / cm or less, for example, 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 -3It is S / cm, and an excellent hybrid separator and a lithium secondary battery including the same can be provided.

[0015] According to one aspect of the present disclosure, even when a flexible polymer layer is formed, the mechanical properties such as the pin piercing strength of 3 N or more and the tensile strength of 100 MPa or more are at the level of an existing polyolefin-based porous substrate, and an excellent hybrid separator and a lithium secondary battery including the same can be provided.

[0016] According to one aspect of the present disclosure, even when the liquid electrolyte is lost during the repeated charge / discharge process, since it serves as a solid electrolyte, a hybrid separator capable of smoothly transferring lithium and a lithium secondary battery including the same can be provided.

[0017] The hybrid separator and the lithium secondary battery of the present disclosure are widely applicable in the fields of electric vehicles, battery charging stations, and other green technologies such as solar power generation and wind power generation using batteries. Further, the hybrid separator and the lithium secondary battery of the present disclosure can be used in eco-friendly electric vehicles, hybrid vehicles, etc. for suppressing air pollution and greenhouse gas emissions to prevent climate change.

Means for Solving the Problems

[0018] One embodiment of the present disclosure is a lithium secondary battery including a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and a liquid electrolyte, wherein the separator is a hybrid separator including a porous substrate and a flexible polymer layer capable of conducting lithium ions disposed on at least one surface of the porous substrate, and the lithium ion conductivity of the hybrid separator is 10 at 25 °C -4 ~10 -2 S / cm, and a lithium secondary battery is provided.

[0019] As one embodiment, a lithium secondary battery includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode and configured to physically separate the positive electrode and the negative electrode while allowing ions to pass through, and a liquid electrolyte disposed between the negative electrode and the positive electrode and configured to transport ions between the positive electrode and the negative electrode. The separator is a hybrid separator including a porous substrate and a flexible polymer layer capable of conducting lithium ions disposed on at least one surface of the porous substrate. The lithium ion conductivity of the hybrid separator is 10 -4 ~10 -2 S / cm at 25°C. A lithium secondary battery is provided.

[0020] As one embodiment, the porosity of the hybrid separator can be 40% or less, but is not limited thereto.

[0021] As one embodiment, the hybrid separator can have a heat shrinkage rate of 30% or less at 150°C, but is not limited thereto.

[0022] As one embodiment, when the thickness of the porous substrate is A and the thickness of the flexible polymer layer is B, B / A can be 1.0 or less, but is not limited thereto.

[0023] As one embodiment, the thickness of the flexible polymer layer on each surface of the hybrid separator can be 0.1 to 5 μm, but is not limited thereto.

[0024] As one embodiment, the porous substrate can be a polyolefin-based porous membrane or a composite membrane having an inorganic particle layer on one or both surfaces of the polyolefin-based porous membrane, but is not limited thereto.

[0025] As one embodiment, the porous substrate can have a thickness of 4 to 25 μm and a porosity of 30 to 70%, but is not limited thereto.

[0026] As one embodiment, the flexible polymer layer can be composed of a crosslinked polymer capable of lithium ion conduction, but is not limited thereto. The "flexible" is distinguished from "non-flexible" or "rigid". Also, "flexible" means the state when it is not disposed on the porous substrate.

[0027] As one embodiment, the flexible polymer layer can include a crosslinked copolymer containing units derived from an acrylic monomer and units derived from an ethylenically unsaturated polyfunctional monomer, but is not limited thereto.

[0028] As one embodiment, the flexible polymer layer can further include any one or two or more additives selected from a lithium salt, a radical additive, and a highly reactive additive.

[0029] As one embodiment, the ethylenically unsaturated polyfunctional monomer can be a polyfunctional acrylate monomer, but is not limited thereto.

[0030] As one embodiment, the ethylenically unsaturated polyfunctional monomer may include one or more selected from the group consisting 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, dianol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and pentaerythritol pentaacrylate, but is not limited thereto.

[0031] As one embodiment, the hybrid separator may have a pin puncture strength of 3 N or more according to ASTM D3763_02 and a tensile strength of 150 to 200 MPa according to ASTM D882, but is not limited thereto.

[0032] As one embodiment, the hybrid separator may have an elongation at break of 20 to 90% at 25°C and an elastic recovery rate of 50 to 100% at a strain of 20%, but is not limited thereto.

[0033] Still other embodiments of the present disclosure are hybrid separators including a porous substrate and a flexible polymer layer capable of lithium ion conduction disposed on at least one surface of the porous substrate, wherein the lithium ion conductivity of the hybrid separator is 10 -4 ~10 -2 S / cm at 25°C.

[0034] As one embodiment, the porous substrate can be a polyolefin-based porous membrane or a composite membrane having an inorganic particle layer on one or both surfaces of the polyolefin-based porous membrane.

[0035] As one embodiment, the flexible polymer layer can be composed of a crosslinked polymer capable of conducting lithium ions.

[0036] As one embodiment, the flexible polymer layer can include a crosslinked copolymer containing units derived from acrylic monomers and units derived from ethylene-based unsaturated polyfunctional monomers, but is not limited thereto.

[0037] As one embodiment, the flexible polymer layer can further include any one or two or more additives selected from lithium salts, radical additives, and highly reactive additives.

Advantages of the Invention

[0038] According to one embodiment of the present disclosure, it is possible to provide an effect of maintaining the ionic conductivity and mechanical strength of the polyolefin-based porous substrate as they are, and suppressing the growth of lithium ion dendrites during repeated charge / discharge processes.

[0039] Also, during repeated charge / discharge processes and during long-term storage of the battery, even if a high-boiling organic solvent is lost and the amount of the liquid electrolyte is lost, since the flexible polymer layer has lithium ion conductivity, the movement of lithium is smooth and the performance of the battery can be maintained for a long time. Therefore, it is possible to provide an advantage that the change in the electrical characteristics of the battery is small even after long-term use.

[0040] In addition, since a flexible polymer layer having flexibility as well as lithium ion conductivity 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 within the same volume, and a high-capacity lithium secondary battery can be provided. The battery cell means a combination of a positive electrode, a negative electrode, and a separator disposed therebetween.

[0041] Moreover, the flexible polymer layer according to an embodiment of the present disclosure is excellent in elasticity, so it serves as a reinforcing material for the separator and has the merit of improving the mechanical properties of the entire separator. In addition, it can not only suppress the growth of lithium dendrites, but also complement the problem that occurs when the dendrites pierce the separator even if the lithium dendrites grow. Due to its elasticity, part of it can be restored to the original state, and damage to the polyolefin-based porous substrate can be minimized. Thereby, the life of the battery can be further improved, and a battery with a lower risk such as explosion can be provided.

[0042] In addition, the thermal shrinkage of the separator can be minimized. During charging / discharging of the battery, the change in thickness can be alleviated to suppress the volume change of the battery, thereby improving the stability of the battery.

[0043] Moreover, the flexible polymer layer contains a crosslinked copolymer having lithium ion conductivity and is also excellent in ion conductivity, so it can play a role similar to that of a liquid electrolyte. Since its reactivity with lithium is lower than that of a liquid electrolyte, it can suppress the increase in resistance due to the depletion of the liquid electrolyte and contribute to the improvement of the life characteristics of the battery.

Mode for Carrying Out the Invention

[0044] Hereinafter, the present disclosure will be described in detail. However, this is merely exemplary, and the present disclosure is not limited to the specific embodiments described exemplarily.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terms used in this disclosure are for the purpose of describing specific embodiments effectively only and are not intended to limit this disclosure.

[0046] Also, unless the context clearly dictates otherwise, the singular forms used in the specification and the appended claims are intended to include the plural forms.

[0047] When a part is described as "including" a certain component, this means that it can further include other components rather than excluding other components, unless there is a specific description to the contrary.

[0048] Also, unless otherwise specifically defined, when a layer or a member is described as being "on" another layer or member, this includes not only the case where a layer or a member is in contact with another layer or member, but also the case where there is still another layer or still another member between the two layers or the two members.

[0049] Also, terms such as "about" and "substantially" used in this disclosure are used in a sense that is the same as or close to the numerical value when the manufacturing and material tolerances inherent in the recited meaning are presented, and are used to prevent unscrupulous infringers from improperly using the disclosed content where exact or absolute numerical values are recited for the purpose of facilitating the understanding of this disclosure.

[0050] The term "(meth)acrylic" used in this disclosure means acrylic or methacrylic.

[0051] As one embodiment, the negative electrode, positive electrode, and liquid electrolyte used in this disclosure can be used without limitation as long as they are those commonly used in this field.

[0052] Hereinafter, each component of the hybrid separator according to one embodiment of this disclosure will be described more specifically.

[0053] [Porous substrate] As one embodiment, the porous substrate can be used without limitation as long as it is commonly used in this field. More specifically, for example, it can be a polyolefin-based porous membrane or a composite membrane having an inorganic particle layer in which inorganic particles are connected to each other on one or both surfaces of the polyolefin-based porous membrane to form pores.

[0054] As one embodiment, the polyolefin-based porous membrane is usually a film or sheet used in this field. For example, it can be a polyolefin-based porous membrane such as polyethylene or polypropylene, but is not limited thereto, and any porous substrate known as a porous substrate for a separator of an electrochemical element can be used.

[0055] As one embodiment, the thickness of the porous substrate can 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 can be any value between the above numerical values. For example, it can be 1 to 100 μm, 3 to 50 μm, 4 to 25 μm, 5 to 20 μm, 5 to 15 μm, 6 to 10 μm, or 9 to 10 μm. Although not limited, the porous substrate can be manufactured by stretching.

[0056] Also, the porosity of the porous substrate can 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 can be any value between the above numerical values. For example, it can be 30 to 70%, 35 to 65%, 40 to 65% or 45 to 65%.

[0057] As another embodiment of the porous substrate, the composite membrane can be a composite membrane in which an inorganic particle layer is formed on a porous membrane made of the polyolefin or the like. The inorganic particle layer can be formed by applying and drying a slurry mixture of inorganic particles and a binder so that the inorganic particles are connected to each other to form pores. The inorganic particle layer can contain a binder and inorganic particles, and can be a porous inorganic particle layer in which the inorganic particles are connected and fixed by the binder to form pores.

[0058] As the inorganic particles, any inorganic particles known as those added for improving the heat resistance of the separator can be used without limitation. Although not limited thereto, for example, any one or a mixture of two or more selected from the group consisting of 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, alumina, mica, zeolite, glass, etc. can be used. Also, as inorganic particles having a dielectric constant of 5 or more, any one or a mixture of two or more selected from the group consisting of SrTiO 3 、SnO 2 、CeO 2 、MgO、NiO、CaO、ZnO、ZrO 2 、Y 2 O 3 、Al 2 O 3 、TiO 2 Or a mixture of one or more selected from the group consisting of SiC or the like can be used. Also, as inorganic particles having piezoelectricity, BaTiO 3 、Pb(Zr、Ti)O 3 (PZT), Pb 1-x La x Zr 1-y Ti y O 3 (PLZT), PB(Mg 3 Nb 2 / 3 )O 3 -PbTiO3 (PMN-PT) or hafnia (HfO 2 ) or any one or more mixtures selected from the group consisting thereof can be used. Further, as the inorganic particles having lithium ion conduction ability, lithium phosphate (Li 3 PO 4 ), lithium titanium phosphate (Li x Ti y (PO 4 ) 3 , 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO 4 ) 3 , 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y -based glass (glass) (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO 3 , 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), SiS 2 (Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4)-based glass or P 2 S 5 (Li x P y S z , 0 < x < 3, 0 < y < 3, 0 < z < 7)-based glass or the like can be used. When the high dielectric constant inorganic particles, the piezoelectric inorganic particles and the inorganic particles having lithium ion conduction ability are used in combination, these enhancing effects can be doubled.

[0059] The size of the inorganic particles is not limited, but the average particle size 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 numerical values. For example, it can be 0.001 - 5 μm, 0.01 - 3 μm, 0.1 - 1 μm, or 0.5 - 1 μm. An inorganic particle layer with a uniform thickness can be formed within the above range to provide an appropriate porosity, but it is not limited thereto. The average particle size means D50, and D50 means the particle size of particles corresponding to 50% in terms of the cumulative fraction based on volume. The average particle size can be derived from the particle size distribution results analyzed using S3500 manufactured by MICROTRAC after sampling a sample in accordance with the ISO 13320-1 standard for the particles to be measured.

[0060] In one embodiment, the thickness of the inorganic particle layer is not limited, but for example, it can be 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 numerical values. For example, it can be 0.1 μm - 5 μm, 0.2 μm - 5 μm, 0.5 μm - 5 μm, 1 μm - 4 μm, or 2 μm - 4 μm, but it is not limited thereto.

[0061] In one embodiment, the inorganic particle layer is disposed on one or both surfaces of the porous membrane, and with respect to 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 entirely on the porous substrate.

[0062] In one embodiment, the inorganic particle layer can be disposed on one or both surfaces of the porous membrane. When the inorganic particle layers are disposed on both surfaces of the porous membrane, the thicknesses of the inorganic particle layers disposed on one surface and the other surface may be the same as each other or different from each other.

[0063] In one embodiment, the binder of the inorganic particle layer can be used as long as it can connect and fix inorganic particles to form a porous inorganic particle layer, and all binders well-known in the art can be used without limitation. Non-limiting examples of the binder include 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), but are not limited thereto.

[0064] The inorganic particle layer can be manufactured by a conventional manufacturing method of disposing an inorganic particle layer known in the art on a porous membrane. For example, water is added to the mixture of the inorganic particles and the binder, and stirred to produce a slurry for the inorganic particle layer. After that, the produced slurry for the inorganic particle layer is applied to one or both sides of the porous membrane by any one of slot die coating, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, and inkjet printing, or a method in which these are combined, and an inorganic particle layer can be formed on the porous membrane.

[0065] [Flexible polymer layer] As one embodiment, the polymer forming the flexible polymer layer can be used without limitation as long as it has flexibility and lithium conductivity. The "flexible" can mean the opposite of "non-flexible" or "rigid". Also, "flexibility" can mean being flexible in a state where it is not disposed on the porous substrate.

[0066] As one embodiment, the flexible polymer layer can be used without limitation as long as it is a polymer having lithium ion conductivity and elasticity. Also, the flexible polymer layer can be composed of a crosslinked polymer capable of conducting lithium ions. For example, it can include a crosslinked copolymer containing units derived from (meth)acrylic monomers and units derived from ethylenically unsaturated polyfunctional monomers.

[0067] As one embodiment, the (meth)acrylic monomer can play a role in the dissociation and transmission of lithium salts and can play a role in improving the ionic conductivity of the flexible polymer layer.

[0068] As one embodiment, the (meth)acrylic monomer may be selected from one or more (meth)acrylic esters such as 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 one or more (meth)acrylic acids such as 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, but is not limited thereto.

[0069] As one embodiment, the ethylenically unsaturated polyfunctional monomer can be a polyfunctional acrylate monomer. In the case of a polyfunctional acrylate monomer, it can play a more excellent role in the dissociation and transmission of lithium salts and can play a role in improving the ionic conductivity of the flexible polymer layer, which is more preferable.

[0070] As an embodiment, the ethylenically unsaturated polyfunctional monomer may include, for example, one or more selected from the group consisting 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, dianol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and pentaerythritol pentaacrylate, but is not limited thereto.

[0071] As an embodiment, by crosslinking the (meth)acrylic monomer and the ethylenically unsaturated polyfunctional monomer in an appropriate ratio, the elasticity of the flexible polymer layer can be further improved. In the above embodiment, the composition ratio of the ethylenically unsaturated polyfunctional monomer in the crosslinked copolymer can be 0.1 to 50 mol% based on the total monomer content, but is not particularly limited as long as it provides a flexible crosslinked polymer. For example, it can be 0.1 mol% or more, 0.5 mol% or more, 1 mol% or more, 5 mol% or more, 50 mol% or less, 40 mol% or less, 30 mol% or less, 20 mol% or less, 10 mol% or less, and can be any value between these. For example, it can be 0.1 to 50 mol%, 1 to 40 mol%, 1 to 30 mol%, 1 to 20 mol%, 1 to 10 mol%.

[0072] As one embodiment, the flexible polymer layer can include, but is not limited to, a polymer obtained by reacting the (meth)acrylic monomer and the ethylenically unsaturated polyfunctional monomer at a weight ratio of 90 to 99:1 to 10. For example, the weight ratio can 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, but is not limited thereto.

[0073] As one embodiment, in order to further improve the elasticity and ionic conductivity of the flexible polymer layer, the following additives can be selectively further included, but are not limited thereto.

[0074] As an additive for the flexible polymer layer, a lithium salt can be selectively further included. After the lithium salt is dissociated by the functional groups of the (meth)acrylic monomer and the ethylenically unsaturated polyfunctional monomer, the anion acts as a nucleophile to further increase the crosslinking degree of the crosslinked copolymer, and the elasticity and other mechanical properties of the flexible polymer layer can be further improved.

[0075] As one embodiment, the lithium salt can be used without limitation as long as it is a lithium salt known in the art. For example, LiPF 6 , LiTFSI, LiFSI, LiBF 4 , LiAsF 6 , LiBOB, LiDFOB, LiClO 4 , LiNO 3 , LiBETI, LiCTFSI, LiB(CN) 4 and the like can be used.

[0076] As one embodiment, the lithium salt can be included in an amount of 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, 20% 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 numerical values, based on the total weight of the flexible polymer layer. For example, it can be included in an amount of 0.1 to 35% by weight, 0.5 to 30% by weight, or 1 to 20% by weight, but is not limited thereto.

[0077] Further, when forming the flexible polymer layer, in addition to the monomer, a radical additive can be selectively further included as an additive. The radical additive helps the initiator to ensure that the crosslinking reaction occurs uniformly even under conditions containing interfering elements of the crosslinking reaction, and can further improve the elasticity and other mechanical properties of the flexible polymer layer.

[0078] Although not limited, examples of the radical additive can further include one or more selected from the group consisting of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl ((2,2,6,6-tetramethylpiperidin-1-yl)oxyl, TEMPO), 4-oxo, 2,2,6,6-tetramethyl-1-piperidine 1-oxyl (4-oxo-2,2,6,6-tetramethyl-1-piperidine 1-oxyl, oxoTEMPO), and di-t-butylnitroxide (DNTBNO).

[0079] As one embodiment, the radical additive can be included in an amount of 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 numerical values, based on the total weight of the flexible polymer layer. For example, it can be included in an amount of 0.1 to 5% by weight, but is not limited thereto. Alternatively, 30 to 60% by weight or 40 to 50% by weight can be used based on the input amount of the initiator, but is not limited thereto.

[0080] In addition, when forming the flexible polymer layer, a highly reactive additive can be selectively further included. The highly reactive additive can enhance the hydrogen bonding force of the crosslinked copolymer, further improve mechanical properties such as the strength of the flexible polymer layer, and increase the crosslinking degree of the crosslinked copolymer.

[0081] As one embodiment, the highly reactive additive can further include one or more selected from the group consisting of carboxylic acid anhydrides, amines, imines, and thiols.

[0082] As one embodiment, examples of the carboxylic acid anhydride include, but are not limited to, maleic anhydride, fumaric anhydride, etc. Examples of the amines include, but are not limited to, poly(N-hydroxyethyl acrylamide) (PHEAA), poly(N-isopropyl acrylamide) (PNIPAM), etc. Examples of the imines include, but are not limited to, polyethylenimine (PEI), etc. The thiols can be compounds containing a thiol group at the terminal, and examples of the thiols include, but are not limited to, 2-ethylhexyl 3-mercaptopropionate, pentaerythritol tetrakis(3-mercaptopropionate), etc.

[0083] As one embodiment, the highly reactive additive can be included in an amount of 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% 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 numerical values, based on the total weight of the flexible polymer layer. For example, it can be included in an amount of 0.1 - 5% by weight, 0.5 - 4% by weight, or 1 - 3% by weight, but is not limited thereto.

[0084] To achieve a high-capacity battery, it is advantageous to thin the separator. Thinning the separator can increase the battery capacity and suppress the growth of dendrites aimed at in the present disclosure. From the perspective of sufficiently improving the elasticity and ion conductivity of the separator, when the thickness of the porous substrate is A and the thickness of the flexible polymer layer is B, B / A can be greater than 0, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.66 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.05 or more, 0.1 or more, 0.15 or more, 0.2 or more, 0.22 or more, and can be any value between the above numerical values. For example, it 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 is the thickness of that one side, and when it is formed on both sides, it means the sum of the thicknesses of each side formed on both sides.

[0085] As one embodiment, the flexible polymer layer can be formed on one or both sides of the porous substrate. Here, the thickness of the flexible polymer layer on each side can be greater than 0 μm, 0.1 μm or more, 0.5 μm or more, 1 μm or more, 2 μm or more, 3 μm or more, 5 μm or less, 4 μm or less, and can be any value between the above numerical values. For example, it can be 0.1 to 5 μm, 0.1 to 4 μm, 0.1 to 3 μm or 0.1 to 2 μm.

[0086] [Hybrid Separator] A hybrid separator according to an embodiment of the present disclosure includes the porous substrate and a flexible polymer layer capable of conducting lithium ions disposed on at least one surface of the porous substrate. At 25 °C, the lithium ion conductivity is -4 S / cm or more, -3 S / cm or more, -2 S / cm or less, and can be any value between the above numerical values. For example, -4 ~ -2 S / cm, -3 ~-2 S / cm, 4.0×10 -3 ~10 -2 S / cm, or 4.0×10 -3 ~7.0×10 -2 S / cm, and to provide an excellent hybrid separator and a lithium secondary battery including the same.

[0087] The hybrid separator according to one embodiment of the present disclosure can satisfy the above range of lithium ion conductivity despite including a flexible polymer layer, and by arranging the flexible polymer layer as the outermost layer, it is possible to suppress the formation of lithium dendrites. More specifically, the lithium ion conductivity of the hybrid separator at 25°C can be calculated by dividing the product of the electrical conduction resistance measured between stainless electrodes and the separator area by the thickness value of the separator after impregnation with a carbonate liquid electrolyte.

[0088] Further, since the flexible polymer layer has elasticity, it can serve as a reinforcing material and has the merit of improving the mechanical properties of the entire separator. Also, it is excellent in ion conductivity and can play a role similar to that of a liquid electrolyte. Also, even if the liquid electrolyte is lost, the flexible polymer layer can play the same role as a solid electrolyte, enabling smooth movement of lithium, extending the life of the battery, and providing a stable battery against ignition and the like. Also, since it has lower reactivity with lithium than a liquid electrolyte, it can suppress an increase in resistance due to depletion of the liquid electrolyte and contribute to improvement of the life characteristics of the battery. Also, during charging / discharging of the battery, it can alleviate the change in thickness and suppress the volume change of the battery, thereby improving the stability of the battery.

[0089] When the flexible polymer layer is formed on the anode or cathode electrode, even if the electrode and the separator are integrated, a spaced space may occur between the electrode and the separator during the electrode assembly process, and lithium dendrites can be formed in this part. However, the hybrid separator according to an embodiment of the present disclosure can be formed in close contact without generating a gap by integrally forming a flexible polymer layer on a porous substrate. Or, some of the flexible polymer layers may be impregnated into the pores from the surface of the porous substrate and integrated. Thereby, no gap occurs even during the electrode assembly process, and the generation of lithium dendrites can be further suppressed.

[0090] A first aspect of the hybrid separator according to an embodiment of the present disclosure may be a polyolefin-based porous membrane and a flexible polymer layer capable of conducting lithium ions laminated on one surface of the polyolefin-based porous membrane.

[0091] A second aspect may be a polyolefin-based porous membrane and a flexible polymer layer capable of conducting lithium ions laminated on both surfaces of the polyolefin-based porous membrane.

[0092] A third aspect is a composite membrane having an inorganic particle layer in which inorganic particles are connected to each other to form pores on one surface of a polyolefin-based porous membrane, and a flexible polymer layer capable of conducting lithium ions laminated on one surface of the composite membrane.

[0093] A fourth aspect is a composite membrane having an inorganic particle layer in which inorganic particles are connected to each other to form pores on one surface of a polyolefin-based porous membrane, and a flexible polymer layer capable of conducting lithium ions laminated on both surfaces of the composite membrane.

[0094] A fifth aspect is a composite membrane having an inorganic particle layer in which inorganic particles are connected to each other to form pores on both surfaces of a polyolefin-based porous membrane, and a flexible polymer layer capable of conducting lithium ions laminated on one surface of the composite membrane.

[0095] The sixth aspect may be a composite membrane having an inorganic particle layer in which inorganic particles are connected to each other on both surfaces of a polyolefin-based porous membrane to form pores, and a flexible polymer layer capable of conducting lithium ions laminated on both surfaces of the composite membrane.

[0096] The first to sixth aspects described a specific example of the present invention and are not limited thereto. Also, other layers can be arranged between the respective layers, and this is not restrictive. Further, in the third to sixth aspects, the inorganic particle layer and the flexible polymer layer may be formed by laminating two or more layers.

[0097] Also, as an embodiment, from the viewpoint of making the porous substrate and the flexible polymer layer adhere better, when using the composite membrane having the inorganic particle layer, after applying a slurry for forming the inorganic particle layer on the porous membrane, the process of drying is not performed, or a flexible crosslinked polymer coating solution is applied to a partially dried (for example, dried with a solvent content of 30% or less) slurry coating layer, so that the interface between the inorganic particle layer and the flexible polymer layer is mixed to form a stronger coating layer.

[0098] Also, at least a part of the pores of the porous substrate can be impregnated and filled with the flexible polymer layer, the interface adheres better, and during the assembly of the battery, no displacement phenomenon occurs, and the formation of lithium dendrites can be suppressed during the charge and discharge process, and the ionic conductivity can be further improved.

[0099] Alternatively, it is also possible to apply a flexible crosslinked polymer coating solution after applying a slurry for forming an inorganic particle layer on the porous membrane and then undergoing a drying process.

[0100] As an embodiment, the total thickness of the hybrid separator 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 numerical values. For example, it can be 3 to 50 μm, 5 to 50 μm, 8 to 40 μm, 10 to 30 μm, or 11 to 15 μm, but is not limited thereto.

[0101] As an embodiment, the porosity of the hybrid separator is not limited. For example, the porosity can 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 can be any value between the numerical values. For example, the porosity can be 5 to 30%, 10 to 25%, 10 to 20%, 13 to 20%, 15 to 20%, but is not limited thereto. Even when the porosity is 20% or less, by adopting a flexible polymer layer capable of lithium movement, it is possible to provide a lithium ion conductivity that is much superior to that of a separator having the same level of porosity without adopting it.

[0102] As described above, the hybrid separator according to an embodiment of the present disclosure has a flexible polymer layer formed thereon, so that the porosity can be lower than that of the porous substrate. However, despite the decrease in porosity, there is an effect that the physical property of having a lithium ion conductivity of 10 -4 ~10 -2 S / cm can be satisfied.

[0103] As one embodiment, the hybrid separator, which is a composite membrane having an inorganic particle layer on one or both surfaces of the porous substrate that is a polyolefin-based porous membrane, can have a heat shrinkage rate at 150 °C of 30% or less, 25% or less, 20% or less, 15% or less, 5% or less, 4% or less, 3% or less. The lower limit is not limited, but can be 0.1% or more, 1% or more, and can be any range between the above-described numerical values. For example, it can be 1 to 30%, 1 to 25%, 1 to 20%, 1 to 10%, 1 to 5%, 1 to 3%, 2 to 25%, 2 to 20%, 2 to 10%, 2 to 5%, 2 to 3%, 5 to 25%, and is not limited thereto. The heat shrinkage rate may vary depending on the type of the porous substrate, and in the case of a composite membrane having an inorganic particle layer on one or both surfaces of the polyolefin-based porous membrane, a lower heat shrinkage rate can be provided compared to the case of the polyolefin-based porous membrane. For example, when the porous substrate is a polyolefin-based porous membrane, the heat shrinkage rate can be 1 to 30%, 5 to 25%, 10 to 20% or 10 to 15%, and in the case of the composite membrane, the heat shrinkage rate can be 1 to 5%, 1 to 3%, 2 to 3%. In the case of a membrane consisting only of the polymer used in the flexible polymer layer of the present disclosure, the heat shrinkage rate can be 50% to 90%, or more, but the hybrid separator according to one embodiment of the present invention can achieve the physical property that the heat shrinkage rate of the final hybrid separator is 30% or less because the porous substrate prevents the heat shrinkage of the flexible polymer layer.

[0104] As one embodiment, the hybrid separator can have a pin puncture strength according to ASTM D3763_02 of 2.5 N or more, 3 N or more, 3.5 N or more, 3.9 N or more, 4.0 N or more, 8 N or less, 7 N or less, 6 N or less, 5 N or less, 4.5 N or less, and can be any value between the above numerical values. For example, it can be 2.5 to 8 N, 3 to 8 N, 3.5 to 8 N, 3.9 to 8 N, 3.9 to 4 N, and is not limited thereto.

[0105] Also, the tensile strength according to ASTM D882 can 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 can be any value between the said numerical values. For example, it can be 80 - 220 MPa, 90 - 210 MPa, 100 - 200 MPa, 130 - 185 MPa, or 180 - 185 MPa, and is not limited thereto.

[0106] As one embodiment, the elongation at break of the hybrid separator at 25°C can be more than 0%, 10% or more, 20% or more, 30% or more, 40% or more, 50% or more, 60% or more, 90% or less, 80% or less, 70% or less, or a value between the said numerical values. For example, it can be 20 - 90%, 30 - 80%, 50 - 80%, 60 - 70%, but is not limited thereto. The elongation at break can be measured according to ASTM D882.

[0107] As one embodiment, the elastic recovery rate of the separator with the flexible polymer layer disposed thereon can be 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, 100% or less, or a value between the said numerical values at a strain of 20%, specifically, it can be 50 - 100%, 50 - 80%, but is not limited thereto. The elastic recovery rate can be calculated by dividing the measured value of the decreased length after removal of the external pressure by the value of the difference between the maximum length increased before removal of the external pressure and the length of the initial sample.

[0108] As one embodiment, the hybrid separator can satisfy all of the above physical property ranges, but is not limited thereto.

[0109] [Manufacturing Method of Hybrid Separator] As long as it is possible to provide a hybrid separator according to an embodiment of the present disclosure, the manufacturing method, conditions, etc. are not limited, but an example will be described. Among the terms described later, if there are terms already described in the above content, the same description can be applied, so the description will be omitted for convenience.

[0110] As an embodiment, taking an example where the porous substrate is a polyolefin-based porous membrane, it can be manufactured by including a step of coating a flexible crosslinked polymer coating solution containing an acrylic monomer, an ethylenically unsaturated polyfunctional monomer, and an initiator on one or both surfaces of the polyolefin-based porous membrane, and subjecting it to photothermal curing such as thermosetting or UV curing to form a flexible polymer layer.

[0111] As an embodiment, when an inorganic particle layer is formed on one or both surfaces of a polyolefin-based porous membrane as the porous substrate, it can be manufactured in two modes.

[0112] That is, the first mode includes a step of applying a slurry for forming an inorganic particle layer on one or both surfaces of the polyolefin-based porous membrane, drying it to form an inorganic particle layer, and coating a flexible crosslinked polymer coating solution containing an acrylic monomer, an ethylenically unsaturated polyfunctional monomer, and an initiator on one or both surfaces of the composite membrane having the inorganic particle layer formed thereon, and subjecting it to thermosetting or UV curing to form a flexible polymer layer. Here, the flexible polymer layer can be formed on the inorganic particle layer.

[0113] In the second mode, when manufacturing a composite membrane having an inorganic particle layer on one or both surfaces of a polyolefin-based porous membrane, after applying a slurry for forming an inorganic particle layer on at least one surface of the polyolefin porous membrane, before drying the slurry coating layer, a flexible crosslinked polymer coating solution containing an acrylic monomer, an ethylenically unsaturated polyfunctional monomer, and an initiator is coated on the upper surface of the slurry coating layer, and after drying, it is thermally cured or UV cured to form a flexible polymer layer. It can be manufactured including this step.

[0114] Also, as an embodiment, before applying the flexible crosslinked polymer coating solution or the slurry for forming the inorganic particle layer to the porous substrate, which is a polyolefin-based porous membrane, the surface of the porous substrate can further include a step of corona discharge treatment and plasma discharge treatment in the atmosphere to perform a hydrophilic treatment. As an example of the method for imparting hydrophilicity to the surface of the porous substrate, in an oxygen and ozone atmosphere such as air, hydroxy groups, carboxy groups, or aldehyde groups can be formed on the surface of the porous substrate by corona discharge or plasma discharge treatment, but chemical treatment is not excluded either.

[0115] As an embodiment, the method for manufacturing the flexible crosslinked polymer coating solution can be provided by utilizing all methods known in the art, and there is no limitation on the means. However, by way of non-limiting example, it can be manufactured by mixing an acrylic monomer, an ethylenically unsaturated polyfunctional monomer, and an initiator without another solvent. Or it is also possible to manufacture it containing a solvent.

[0116] As the initiator, any initiator commonly used in the industry can be used without limitation as long as it is a thermal polymerization initiator or a UV curing type initiator. Examples of thermal polymerization initiators include, but are not limited to, azo compounds, organic peroxides, and hydrogen peroxide.

[0117] As one embodiment, when the acrylic monomer and the ethylenically unsaturated polyfunctional monomer are contained in a flexible crosslinked polymer coating solution in an appropriate ratio and crosslinked, the elasticity of the produced flexible polymer layer can be further improved. In the above embodiment, the molar ratio of the acrylic monomer to the ethylenically unsaturated polyfunctional monomer in the flexible crosslinked 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 numerical values. Specifically, it can be a molar ratio of 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.

[0118] For example, the flexible crosslinked polymer coating solution can contain a monomer mixture in which the acrylic monomer and the ethylenically unsaturated polyfunctional monomer are mixed at a weight ratio of 90 to 99:1 to 10 and an initiator. The initiator can be contained in an amount of 0.1 to 5% by weight, but is not limited thereto.

[0119] In order to provide a flexible polymer layer with further improved elasticity and ion conductivity, according to a specific embodiment, the flexible crosslinked polymer coating solution can optionally further contain the following additives, but is not limited thereto. Since the same explanations as those above can be applied to the reasons for adding the additives and the types of additives, the explanations are omitted for convenience.

[0120] As one embodiment, the flexible crosslinked polymer coating solution can optionally further contain a lithium salt. The lithium salt can be contained in an amount of 30% by weight or less, 25% by weight or less, 20% 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 numerical values, based on the total weight of the solid content of the flexible crosslinked polymer coating solution. Specifically, it can be contained in an amount of 0.1 to 30% by weight, 0.5 to 25% by weight, or 1 to 20% by weight, but is not limited thereto.

[0121] As one embodiment, the flexible crosslinked polymer coating solution may further selectively include a radical additive. For example, it may further include one or more selected from the group of radical additives such as (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).

[0122] As one embodiment, the radical additive may be included in an amount of 30% by weight or less, 25% by weight or less, 20% 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 numerical values, based on the total weight of the solid content of the flexible crosslinked polymer coating solution. Specifically, it may be included in an amount of 0.1 to 30% by weight, 0.5 to 25% by weight, or 1 to 20% by weight, but is not limited thereto.

[0123] As one embodiment, the flexible crosslinked polymer coating solution may further selectively include a highly reactive additive. More specifically, it may further include one or more selected from the group consisting of carboxylic acid anhydrides, amines, imines, and thiols.

[0124] As one embodiment, the highly reactive additive may be included in an amount of 30% by weight or less, 25% by weight or less, 20% 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 numerical values, based on the total weight of the solid content of the flexible crosslinked polymer coating solution. For example, it may be included in an amount of 0.1 to 30% by weight, 0.5 to 25% by weight, or 1 to 20% by weight, but is not limited thereto.

[0125] As one embodiment, the slurry for forming the inorganic particle layer can utilize all methods known in the art and is not limited.

[0126] As one embodiment, as a non-limiting example of the coating process, any one of slot die coating, roll coating, spin coating, dip coating, bar coating, die coating, slit coating, and inkjet printing, or a method in which these are combined, can be utilized.

[0127] As one embodiment, in the step of forming the flexible polymer layer, after applying the composition, it can be heated to perform drying and crosslinking reactions. As a specific embodiment for performing the drying and crosslinking reactions more smoothly, the heating temperature can be 40°C or higher, 50°C or higher, 60°C or higher, 65°C or higher, 150°C or lower, 120°C or lower, 100°C or lower, 90°C or lower, 80°C or lower, or a value between the above numerical values. For example, it can be 40 to 150°C, 50 to 120°C, 60 to 100°C, 60 to 90°C, or 65 to 80°C, but is not limited thereto.

[0128] As one embodiment, the heating time for performing the drying and crosslinking reactions more smoothly can be 1 minute or longer, 5 minutes or longer, 10 minutes or longer, 20 minutes or longer, 30 minutes or longer, 3 hours or shorter, 2 hours or shorter, 1 hour or shorter, or a value between the above numerical values. For example, it 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.

[0129] As one embodiment, although not limited to the heating atmosphere, for example, it can be an air atmosphere or preferably an atmosphere without moisture and oxygen.

[0130] As one embodiment, the method of providing the inorganic particle layer on the porous membrane may be manufactured by an ordinary manufacturing method without limitation. As a non-limiting example, water may be added to a mixture of inorganic particles and a binder, and stirred to produce a slurry for the inorganic particle layer, or a slurry obtained by mixing inorganic particles and water without a binder may be produced and used. The produced slurry for the inorganic particle layer may be applied to one or both surfaces of the porous membrane 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, to provide an inorganic particle layer on at least one surface of the porous membrane.

[0131] As one embodiment, a lithium battery including the separator of the above-described embodiment can be provided. The lithium battery can refer to all electrochemical elements containing lithium, and in particular, its type is not limited. As a non-limiting example of a lithium battery, a lithium secondary battery can be mentioned. Since the lithium secondary battery is well-known and its configuration is also well-known, it will not be specifically described in the present disclosure.

[0132] As one embodiment, the lithium battery can include a positive electrode, a negative electrode, and the hybrid separator of the present embodiment interposed between the positive electrode and the negative electrode. Here, any of the positive electrode and the negative electrode can be used without limitation as long as they are those usually used in a lithium secondary battery.

[0133] Hereinafter, the embodiments of the present disclosure will be further described with reference to specific experimental examples. The examples and comparative examples included in the experimental examples illustrate the present disclosure and do not limit the scope of the appended claims. It is obvious to those skilled in the art that various changes and modifications to the examples are possible within the scope of the present disclosure and the scope of the technical idea, and it is natural that such deformations and modifications belong to the scope of the appended claims.

[0134] The physical properties were measured as follows.

[0135] <Ionic conductivity> The ionic conductivity of the hybrid separators in each example and comparative example was calculated from the following mathematical formula.

[0136] Ionic conductivity = L ÷ (R × A)

[0137] Here, L = the thickness of the hybrid separator impregnated with the liquid electrolyte (unit: cm) R = the impedance value of the hybrid separator impregnated with the liquid electrolyte at 25°C (unit: Ω = 1 / S) (the real part value when the imaginary part value of the impedance is 0) A = the overlapping area between the two electrodes during impedance measurement (cm 2 ) Ionic conductivity = L ÷ (R × A)

[0138] For the determination of the R value, after punching out the hybrid separator into a concentric circle with a diameter of 18 mm, it was impregnated with a carbonate liquid electrolyte (1 M LiPF 6 in EC / EMC / DEC 3:5:2 (v / v / v)) for 1 hour. Here, the L value was measured with a micrometer manufactured by Mitutoyo, and the A value was determined to be 2.5447 cm 2 Then, a 2032 standard coin cell (SUS material) was assembled as a separator impregnated with the liquid electrolyte, and a constant voltage impedance measurement was performed in the range of 100 MHz to 100 MHz under the conditions of an initial voltage of 0 V and an amplitude of 5 mV using an IM6 equipment manufactured by Zahner. The impedance value R of the real part when the value of the imaginary part was 0 was obtained by measuring the impedance equivalent circuit fitting of the measured impedance.

[0139] <Porosity> The porosity of the separator was calculated from the following mathematical formula by cutting a rectangular sample of A cm × B cm. Both A and B were cut and measured in the range of 5 to 20 cm respectively.

[0140] Porosity = {(A × B × T) - (M ÷ ρ) ÷ (A × B × T)} × 100

[0141] Here, T = Thickness of the separator (cm) M = Weight of the sample (g) ρ = True density of the entire separator (g / cm 3 )

[0142] <Thermal shrinkage rate> After cutting the separator into a square shape with a side length of 10 cm to produce a sample, the area of the sample before the experiment was measured and recorded using a camera. Five sheets of paper were placed on top of and below the sample so that the sample was centered, and the four sides of the paper were fixed with clips. The sample wrapped in paper was left in a hot air circulation dryer at 150 °C for 1 hour. When the leaving was completed, the sample was taken out, and the changes in the lengths of the MD and TD directions of the separator were measured with a camera respectively, and the shrinkage rate was calculated using the following mathematical formula. The values in the MD and TD directions were obtained respectively, and the average value was recorded.

[0143] Shrinkage rate (%) = (Length of one side of the sample before heating (L 0 ) - Length of one side of the deformed sample after heating (L)) ÷ Length of one side of the sample before heating (L 0 ) × 100

[0144] <Pin puncture strength> The pin puncture strength of the separator was measured according to ASTM D3763_02.

[0145] <Tensile strength and elongation at break> The tensile strength and elongation at break of the separator were measured at 25 °C according to ASTM D882. The values in the MD and TD directions were obtained respectively, and the average value was recorded.

[0146] <Elastic recovery rate> The elastic recovery rate value of the separator was calculated by the change rate of the integral area of the curve obtained after performing a tensile test using a Universal Testing Machine.

[0147] Elastic recovery rate (%) = (X) ÷ (Y) × 100

[0148] X = Integral area of the stress-strain curve obtained when applying tensile force to the test piece Y = Integral area of the stress-strain curve obtained when removing the tensile force

[0149] Here, to determine the X value and Y value, a test piece with a size of 60 mm × 10 mm (length × width respectively) is prepared. The distance L between the clamps of the universal testing machine 0 is set to clamp the test piece so that it becomes 40 mm, and while stretching the test piece at a speed of 100 mm / min so that the final length L becomes 48 mm, a stress-strain curve for determining the X value is obtained. Immediately after that, an external force is removed to return to the initial length, and a stress-strain curve for determining the Y value is obtained. From the obtained X and Y values, the value of the elastic recovery rate is calculated.

[0150] <Thickness> The thickness of the separator was measured using a contact-type thickness measuring instrument with an accuracy of 0.1 μm with respect to the thickness.

[0151] <Gurley permeability> The Gurley permeability of the porous substrate was measured using a Densometer manufactured by Toyoseiki Co., Ltd. in accordance with ASTM D726 standard. The time taken for 100 cc of air to pass through an area of 1 square inch of the porous substrate was recorded in seconds and compared.

[0152] <Presence or absence of lithium dendrite generation in the battery> Li(Ni 0.8 Co 0.1 Mn 0.1 )O 2 Between the positive electrode of ()O and the graphite negative electrode, separators manufactured in the examples and comparative examples were placed to assemble a single-plate battery. The battery was filled with 1.15M LiPF6 A liquid electrolyte in which 6 is dissolved together with 5 wt% FEC (Fluoroethylene Carbonate) in an EC (ethylene carbonate) / EMC (ethyl methyl carbonate) / DEC (diethyl carbonate) (3:5:2, v / v / v) mixed solvent is injected. The battery is charged and discharged in a CC / CV mode at a current density of 0.5C within a voltage range of 3.0V to 4.2V for 100 cycles, and then decomposed in a charged state to confirm the presence or absence of the generation and growth of lithium dendrites. After recovering the negative electrode from the battery decomposed in an environment free from exposure to oxygen and moisture, the remaining lithium salt is washed with an EC / EMC / DEC mixed solvent and then dried. The surface of the dried negative electrode is observed visually and by SEM to confirm the presence or absence of lithium dendrites in the battery. <Molecular weight> The weight average molecular weight (Mw) and the number average molecular weight (Mn) are polystyrene-equivalent molecular weights measured by Gel Permeation Chromatography (GPC) using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard substances.

[0153] [Production Example 1] Production of Aqueous Slurry for Inorganic Particle Layer After adding 1.0 part by weight of a carboxylic acid polymer-based inorganic dispersant (Dispex (registered trademark) AA 4030, manufactured by BASF) to 100 parts by weight of distilled water, 100 parts by weight of boehmite (γ-AlO(OH)) with an average particle size of 500 nm is added and stirred, and dispersed with a bead mill to produce a uniform aqueous slurry base solution. Acrylic polymer (manufactured by Sigma-Aldrich, CAS No.: 9003-05-8, M n: 150,000) 50 parts by weight of a 10% aqueous solution was added with respect to the amount of boehmite charged, and 40 parts by weight of distilled water was further added and diluted to a viscosity suitable for the target coating thickness, followed by stirring. Before coating, 1,000 ppm of a wetting additive (TEXAPON (registered trademark) SB 3 UNKONS manufactured by BASF) was added with respect to the weight of the entire solution, and then stirred for an additional 1 hour to produce an aqueous slurry for the inorganic particle layer.

[0154] [Production Example 2] Production of Flexible Crosslinked Polymer Coating Solution (1) 95% by weight of butyl methacrylate, 4% by weight of poly(ethylene glycol) dimethacrylate with a number average molecular weight (Mn) of 550 g / mol, and 1% by weight of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to produce a flexible crosslinked polymer coating solution. The produced solution was stored in a refrigerated environment at 5°C or lower and consumed in the coating and crosslinking reactions within 2 hours of production.

[0155] [Production Example 3] Production of Flexible Crosslinked Polymer Coating Solution (2) 95% by weight of butyl methacrylate, 4% by weight of poly(ethylene glycol) dimethacrylate with Mn of 550 g / mol, and 1% by weight of an initiator (2-hydroxy-2-methylpropiophenone) were mixed to produce a base solution of a flexible crosslinked polymer coating solution. Next, a lithium salt obtained by mixing lithium bis(fluorosulfonyl)imide and lithium difluoro(oxalate)borate in a weight ratio of 8:2 was mixed at 20% by weight (20 mol% with respect to the amount of butyl methacrylate charged) with respect to the weight of the entire polymer to produce a flexible crosslinked polymer coating solution. The produced solution was stored in a refrigerated environment at 5°C or lower and consumed in the coating and crosslinking reactions within 2 hours of production.

[0156] [Production Example 4] Production of Flexible Crosslinked Polymer Coating Solution (3) 95 wt% butyl methacrylate, 4 wt% poly(ethylene glycol) dimethacrylate with Mn 550 g / mol, and 1 wt% initiator (2-hydroxy-2-methylpropiophenone) were mixed to produce a base solution of a flexible crosslinked polymer coating solution. Next, as a radical additive, (2,2,6,6-tetramethylpiperidin-1-yl)oxyl was mixed in an amount of 50 wt% based on the amount of the initiator added to produce a flexible crosslinked polymer coating solution. The prepared solution was stored in a refrigerated environment at 5°C or lower and consumed in coating and crosslinking reactions within 2 hours of production.

[0157] [Production Example 5] Production of Flexible Crosslinked Polymer Coating Solution (4) 95 wt% butyl methacrylate, 4 wt% poly(ethylene glycol) dimethacrylate with Mn 550 g / mol, and 1 wt% initiator (2-hydroxy-2-methylpropiophenone) were mixed to produce a base solution of a flexible crosslinked polymer coating solution. Next, as a highly reactive additive, maleic anhydride was mixed in an amount of 3 wt% based on the flexible crosslinked polymer coating solution base to produce a flexible crosslinked polymer coating solution. The prepared solution was stored in a refrigerated environment at 5°C or lower and consumed in coating and crosslinking reactions within 2 hours of production.

[0158] [Example 1] Production of Hybrid Separator (1) As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0159] The flexible crosslinked polymer coating solution produced in Production Example 2 was applied to both sides of the porous substrate by a bar coating method, followed by hot air drying, and then exposed to metal halide lamp light in a UV crosslinking apparatus in which the oxygen concentration was adjusted to 500 ppm or less by nitrogen purging to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm each.

[0160] The total thickness of the manufactured hybrid separator was 11 μm, and its physical properties were evaluated and shown in Table 1 below.

[0161] [Example 2] Manufacture of Hybrid Separator (2) As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0162] For the inorganic particle layer coating, both sides of the porous film were subjected to corona discharge treatment to introduce surface polar groups. Here, the corona surface treatment was carried out at a speed of 5 mpm (meter per minute).

[0163] After coating both sides of the porous substrate with the aqueous slurry manufactured in Production Example 1, drying was performed to form an inorganic particle layer. After drying, the thickness of the inorganic particle layer formed on both sides was 2 μm each.

[0164] After applying the flexible crosslinked polymer coating solution manufactured in Production Example 2 on top of the inorganic particle layers on both sides, hot air drying was performed, and then it was exposed to the metal halide lamp light in a UV crosslinking device where the oxygen concentration was adjusted to 500 ppm or less by nitrogen purging to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm each.

[0165] The total thickness of the manufactured hybrid separator was 15 μm, and its physical properties were evaluated and shown in Table 1 below.

[0166] [Example 3] Manufacture of Hybrid Separator (3) In Example 1 above, it was manufactured in the same manner as Example 1 except that the thickness of the flexible polymer layer was adjusted so that each thickness became 3 μm. The total thickness of the manufactured hybrid separator was 15 μm, and its physical properties were evaluated and shown in Table 1 below.

[0167] [Example 4] Manufacture of Hybrid Separator (4) As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0168] On both sides of the porous substrate, the flexible crosslinked polymer coating solution produced in Production Example 3 was applied, followed by hot air drying, and exposure to metal halide lamp light in a UV crosslinking apparatus in which the oxygen concentration was adjusted to 500 ppm or less by nitrogen purging to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm each.

[0169] The total thickness of the produced hybrid separator was 11 μm, and its physical properties were evaluated and shown in Table 1 below.

[0170] [Example 5] Production of Hybrid Separator (5) As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0171] On both sides of the porous substrate, the flexible crosslinked polymer coating solution produced in Production Example 4 was applied, followed by hot air drying, and exposure to metal halide lamp light in a UV crosslinking apparatus in which the oxygen concentration was adjusted to 500 ppm or less by nitrogen purging to form a flexible polymer layer. The thickness of the flexible polymer layer formed on both sides was 1 μm each.

[0172] The total thickness of the produced hybrid separator was 11 μm, and its physical properties were evaluated and shown in Table 1 below.

[0173] [Example 6] Production of Hybrid Separator (6) As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0174] After applying the flexible crosslinked polymer coating solution produced in Production Example 5 to both sides of the porous substrate, it was dried with hot air and exposed to metal halide lamp light in a UV crosslinking apparatus in which the oxygen concentration was adjusted to 500 ppm or less by nitrogen purging to form a flexible polymer layer. The thickness of the flexible polymer layers formed on both sides was 1 μm each.

[0175] The total thickness of the produced hybrid separator was 11 μm, and its physical properties were evaluated and shown in Table 1 below.

[0176] [Comparative Example 1] The flexible crosslinked polymer coating solution of Production Example 2 was applied and cured on a single Teflon (registered trademark) sheet to produce a flexible polymer sheet with a thickness of 19 μm.

[0177] The physical properties of the flexible polymer sheet thus produced were evaluated and shown in Table 1 below.

[0178] [Comparative Example 2] A separator was produced in the same manner as in Example 2 except that no flexible polymer layer was formed.

[0179] As the porous substrate, a polyethylene porous film with a thickness of 9 μm, a porosity of 45%, and a Gurley permeability of 70 sec / 100 cc was used.

[0180] For the coating of the inorganic particle layer, both sides of the porous film were treated with corona discharge to introduce surface polar groups. Here, the corona surface treatment was carried out at a speed of 5 mpm (meter per minute).

[0181] After coating the aqueous slurry produced in Production Example 1 on both sides of the porous substrate, it was dried to form an inorganic particle layer. After drying, the thickness of the inorganic particle layers formed on both sides was 2 μm each.

[0182] The total thickness of the produced separator was 13 μm, and its physical properties were evaluated and shown in Table 1 below.

[0183] [Comparative Example 3] In Example 1, the same procedure was carried out except that the flexible polymer layer was repeatedly coated to produce a separator with a coating thickness of 5 μm on one side. The results are summarized in Table 1.

[0184] [Table 1]

[0185] As shown in Table 1 above, although the porosity, which is the volume ratio occupied by pores that are the lithium ion migration path in the entire separator, is 20% or less in the above Example, in terms of lithium ion conductivity, it was confirmed that it has excellent lithium ion conductivity at almost the same level as Comparative Example 2 where there is no flexible polymer film and the porosity is as high as 45%.

[0186] At the same time, it was confirmed that the elastic recovery rate for suppressing the growth of lithium dendrites inside the battery increased to 50% or more, and the pin piercing strength and tensile strength had excellent mechanical physical properties such as being the same or maintaining a high level.

[0187] Also, as in Example 2, when further including an inorganic particle layer, it was possible to confirm that the thermal shrinkage rate was lower.

[0188] Also, as in Comparative Example 1, when consisting only of a flexible polymer sheet without a polyolefin-based porous membrane, it was confirmed that the thermal shrinkage rate was high, the ion conductivity was low, and the mechanical physical properties were not good.

[0189] Comparative Example 2 is a case where inorganic particle layers are formed on both sides of a polyolefin-based porous membrane as a separator in a conventionally used form. However, it was found that the Examples of the present disclosure have the same level of conductivity without showing a difference in lithium ion conductivity compared to Comparative Example 2 despite having a lower porosity, and have a remarkable improvement in physical properties in terms of elastic recovery rate.

[0190] Also, as shown in Comparative Example 3, it was found that when B / A exceeds 1.0, the porosity and lithium ion conductivity significantly decrease.

[0191] That is, in Examples 1 to 6 according to one embodiment of the present disclosure, although the porosity of the first polyolefin-based porous film is 45%, which is a porosity level of 20% or less, the porosity is lower, but the ion conductivity is at the same level as that of a conventional separator without a flexible polymer layer as in Comparative Example 2. It was confirmed. In addition, it was confirmed that it has excellent mechanical strength and elastic recovery rate. Further, after assembling the battery and repeating charging and discharging 100 times, when the presence or absence of lithium dendrite formation was confirmed, it was confirmed that the degree of lithium dendrite generation was surely reduced compared to Comparative Example 2.

[0192] Also, as shown in Example 2, when an inorganic particle layer is formed on the porous substrate, it was confirmed that the physical property that the thermal shrinkage rate is 5% or less at 150 °C can be satisfied.

[0193] The above content is merely an exemplification of applying the principle of the present disclosure, and other configurations may be further included without departing from the scope of the present invention.

[0194] As described above, in the present invention, specific matters and limited examples are described, but this is provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples. For those having ordinary knowledge in the field to which the present invention pertains, various modifications and variations are possible from such descriptions.

[0195] Therefore, the idea of the present invention should not be defined only by the above-described examples, and not only the scope of the following claims, but also all those having equivalent or equivalent modifications to the scope of the present claims 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 including a porous substrate and a flexible polymer layer capable of conducting lithium ions disposed on at least one surface of the porous substrate; The lithium ion conductivity of the hybrid separator is 10 －４ ~10 －２ A lithium secondary battery having a specific electrical conductivity of 1.0 S / cm.

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

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

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

5. 5. The lithium secondary battery according to claim 4, wherein the thickness of the flexible polymer layer on each side of the hybrid separator is 0.1 to 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 to 25 μm and a porosity of 30 to 70%.

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

9. 9. The lithium secondary battery of claim 8, wherein the flexible polymer layer comprises a cross-linked copolymer including units derived from an acrylic monomer and units derived from an ethylenically unsaturated polyfunctional monomer.

10. The lithium secondary battery according to claim 8 , wherein the flexible polymer layer further comprises one or more additives selected from the group consisting of a lithium salt, a radical additive, and a highly reactive additive.

11. The lithium secondary battery according to claim 9 , wherein the ethylenically unsaturated polyfunctional monomer is a polyfunctional acrylate monomer.

12. 12. The lithium secondary battery of claim 11, wherein the ethylenically unsaturated polyfunctional monomer comprises one or more selected from the group consisting 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, dianol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, and pentaerythritol pentaacrylate.

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

14. 2. The lithium secondary battery according to claim 1, wherein the hybrid separator has a breaking elongation of 20 to 90% at 25° C. and an elastic recovery rate at 20% strain of 50 to 100%.

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

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

17. 16. The hybrid separator of claim 15, wherein the flexible polymer layer is comprised of a cross-linked polymer capable of conducting lithium ions.

18. 20. The hybrid separator of claim 17, wherein the flexible polymeric layer comprises a crosslinked copolymer comprising units derived from an acrylic monomer and units derived from an ethylenically unsaturated polyfunctional monomer.

19. 20. The hybrid separator of claim 17, wherein the flexible polymer layer further comprises one or more additives selected from the group consisting of lithium salts, radical additives, and highly reactive additives.

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