Electrode for lithium secondary battery, method for producing same, and lithium secondary battery including same

Abstract

The present invention relates to an electrode for a lithium secondary battery, the electrode comprising: an electrode substrate; a first porous layer formed on the electrode substrate and having a porosity of 10% or less; and a second porous layer formed on the first porous layer, containing a binder resin and inorganic fine particles, and having a porosity of 30% or more; a manufacturing method thereof, and a lithium secondary battery comprising the same.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0063562, filed May 24, 2022, and Korean Patent Application No. 10-2023-0062527, filed May 15, 2023, and all contents disclosed in the documents of these Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to an electrode for a lithium secondary battery, which includes a porous layer formed on the electrode and can achieve high insulating properties and low resistance properties, a method for manufacturing the same, and a lithium secondary battery including the same. [Background technology]

[0003] In recent years, with the increasing technological development and demand for mobile devices, the demand for rechargeable secondary batteries as an energy source has skyrocketed, and as a result, much research is being conducted on secondary batteries that can meet various requirements. Secondary batteries are also attracting attention as a power source for electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (Plug-in HEVs), which have been proposed as a solution to address air pollution caused by conventional gasoline and diesel vehicles that use fossil fuels.

[0004] In lithium secondary batteries, if a short circuit occurs due to contact between the positive and negative electrodes, it can cause severe heat generation and explosion. The porous separators used in secondary batteries exhibit severe thermal shrinkage at temperatures above 100°C due to material properties and manufacturing process characteristics, including stretching, which can lead to short circuits between the positive and negative electrodes. To address this battery safety issue, a separator has been proposed that incorporates a porous coating layer made of a mixture of insulating filler particles and a binder polymer on a porous substrate, with a substance with a shutdown function added to the porous coating layer.

[0005] However, in the case of conventional separators in which a porous coating layer having inorganic particles is formed on a porous substrate, there is no separate adhesive layer, which results in weak interfacial adhesion with the counter electrode, reducing the ease of battery assembly. In addition, there are problems with interfacial peeling occurring due to the lack of adhesion as the electrodes expand and contract, resulting in reduced battery life.

[0006] Therefore, there is a need for research into lithium secondary batteries that include separators that achieve excellent adhesive strength and battery life characteristics. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides an electrode for a lithium secondary battery that achieves high insulating properties and low resistance properties.

[0008] The present invention also provides a method for producing the electrode for a lithium secondary battery.

[0009] The present invention also provides a lithium secondary battery including the above-mentioned electrode for a lithium secondary battery. [Means for solving the problem]

[0010] The present invention provides an electrode for a lithium secondary battery, comprising: an electrode substrate; a first porous layer formed on the electrode substrate and having a porosity of 10% or less; and a second porous layer formed on the first porous layer, comprising a binder resin and inorganic fine particles, and having a porosity of 30% or more.

[0011] The present invention also provides a method for manufacturing an electrode for a lithium secondary battery, comprising the steps of: applying a composition for forming a first porous layer onto an electrode substrate and drying the composition to form a first porous layer on at least one surface of the electrode substrate; and applying a composition for forming a second porous layer, the composition including a binder resin and inorganic fine particles, onto the first porous layer and drying the composition to form a second porous layer, wherein the first porous layer has a porosity of 10% or less, and the second porous layer has a porosity of 30% or more.

[0012] The present invention also provides a lithium secondary battery including the electrode for a lithium secondary battery.

[0013] Hereinafter, an electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery including the same according to embodiments of the present invention will be described in detail.

[0014] The terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of ​​the invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his or her invention.

[0015] Unless otherwise defined herein, all technical and scientific terms have the same meaning as commonly understood by those of ordinary skill in the art to which this invention belongs. The terms used in describing the present invention are merely for the purpose of effectively describing specific embodiments and are not intended to limit the present invention.

[0016] As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise.

[0017] As used herein, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements and / or components and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components and / or groups.

[0018] Since the present invention can be modified in various ways and can have various forms, specific examples are exemplified and described in detail below, but it is not intended to limit the present invention to the particular disclosed form, and it should be understood that the present invention includes all modifications, equivalents, and alternatives falling within the spirit and technical scope of the invention.

[0019] In this specification, when the positional relationship of two parts is described using terms such as "above," "on top," "below," or "beside," one or more other parts may be located between the two parts, unless the terms "immediately" or "directly" are used.

[0020] In this specification, when a temporal relationship is described using terms such as "after," "following," "next," or "before," it may also include cases where the relationship is not consecutive, unless the terms "immediately" or "directly" are used.

[0021] As used herein, the term "at least one" should be understood to include all possible combinations of one or more of the associated items.

[0022] According to one embodiment of the invention, there is provided an electrode for a lithium secondary battery, comprising: an electrode substrate; a first porous layer formed on the electrode substrate and having a porosity of 10% or less; and a second porous layer formed on the first porous layer, comprising a binder resin and inorganic fine particles, and having a porosity of 30% or more.

[0023] In conventional lithium secondary batteries, the separator between the positive and negative electrodes includes a porous substrate and a first porous layer formed on the porous substrate. This means there is no separate adhesive layer, resulting in weak interfacial adhesion with the opposing electrode, which reduces the efficiency of the battery assembly process. Furthermore, the expansion and contraction of the electrodes causes insufficient adhesion, which leads to interfacial peeling, thereby reducing the battery's lifespan.

[0024] Therefore, the inventors have found that the above problem can be solved by including a first porous layer having a porosity of 10% or less and a second porous layer having a porosity of 30% or more, which includes a first binder resin and inorganic microparticles, instead of a porous polymer separation membrane including a porous substrate and a coating layer formed on the porous substrate, which has been used as a separation membrane in the past.

[0025] Specifically, the inventors have confirmed through experiments that since the separator used in a lithium secondary battery is formed directly on the electrode substrate without a porous substrate, by coating a first porous layer with low porosity on the interface that contacts the electrode, the interfacial contact area is increased, and adhesive strength is maintained even when the electrode expands and contracts, thereby achieving excellent battery life characteristics, and have completed the invention.

[0026] Furthermore, the inventors have confirmed through experiments that the electrode for a lithium secondary battery of the present invention comprises a first porous layer formed on an electrode substrate and having a porosity of 10% or less; and a second porous layer formed on the first porous layer, comprising a binder resin and inorganic fine particles, and having a porosity of 30% or more. This demonstrates that the dense structure of the first porous layer with low porosity prevents the inorganic fine particles and binder resin of the second porous layer, which are generated during drying, from migrating to the interface with the lower electrode, thereby suppressing an increase in resistance at the electrode interface, and that low resistance characteristics can also be achieved by the ion-conductive binder resin in the first porous layer. This led to the completion of the invention.

[0027] The electrode for a lithium secondary battery may be a positive electrode for a lithium secondary battery or a negative electrode for a lithium secondary battery.

[0028] In the electrode for a lithium secondary battery of the embodiment, the difference in porosity between the first porous layer and the second porous layer may be 20% or more.

[0029] The difference between the porosity of the first porous layer and the porosity of the second porous layer can be calculated by the following Equation 1.

[0030] [Formula 1] Difference (%) between the porosity of the first porous layer and the porosity of the second porous layer = Porosity (%) of the second porous layer - Porosity (%) of the first porous layer

[0031] The difference in porosity between the first porous layer and the second porous layer may be specifically 20% or more, 30% or more, 40% or more, 50% or more, 99% or less, 90% or less, 80% or less, 70% or less, 60% or less, or 55% or less, and may be 20% or more and 99% or less, 20% or more and 90% or less, 20% or more and 80% or less, 20% or more and 70% or less, 20% or more and 60% or less, 20% or more and 55% or less, 30% or more and 99% or less, or 30% or more and 90% It may be 30% or more and 80% or less, 30% or more and 70% or less, 30% or more and 60% or less, 30% or more and 55% or less, 40% or more and 99% or less, 40% or more and 90% or less, 40% or more and 80% or less, 40% or more and 70% or less, 40% or more and 60% or less, 40% or more and 55% or less, 50% or more and 99% or less, 50% or more and 90% or less, 50% or more and 80% or less, 50% or more and 70% or less, 50% or more and 60% or less, or 50% or more and 55% or less.

[0032] When the difference in porosity between the first porous layer and the second porous layer is 20% or more, excellent battery characteristics and insulating characteristics can be achieved.

[0033] If the difference in porosity between the first porous layer and the second porous layer is less than 20%, the porosity of the first porous layer may be too high, making ion conduction difficult, or the porosity of the second porous layer may be too low, increasing resistance during ion conduction.

[0034] Furthermore, if the difference in porosity between the first porous layer and the second porous layer is too large, a technical problem may occur in that the insulating properties are reduced due to an increase in empty spaces with a low dielectric constant.

[0035] Specifically, in the electrode for a lithium secondary battery according to the embodiment, the second porous layer may have a porosity of 30% or more, 30% to 90% or less, 40% to 90% or less, 40% to 80% or less, 40% to 70% or less, 40% to 60% or less, or 50% to 60% or less.

[0036] The porosity of the second porous layer can be achieved depending on the composition of the second porous layer, which will be described later. When the porosity of the second porous layer is 30% or more and 90% or less, the effect of enabling ion conduction through the pores can be achieved.

[0037] If the porosity of the second porous layer is less than 30%, the resistance during ion conduction may be large, and if the porosity of the second porous layer is more than 90%, a technical problem may occur in that the insulating properties may be reduced due to an increase in empty spaces with a low dielectric constant.

[0038] The porosity can be calculated from the density / ratio of inorganic fine particles in the slurry, the density / ratio of binder, and the measured weight (loading amount) and thickness of the sample.

[0039] Alternatively, the porosity can be calculated by the following Equation 2 using the ratio of the density obtained by measuring the volume and mass of the second porous layer of a sample coated with the composition on an electrode of a certain area to the theoretical density of the solid content of the coating composition.

[0040] [Formula 2] Porosity (%) = {1-(actual density) / (theoretical density)} x 100

[0041] Specifically, in the lithium secondary battery electrode of the embodiment, the first porous layer may have a porosity of 10% or less, 0.01% or more, 0.1% or more, 1% or more, 5% or more, or 7% or more, or 0.01% to 10% or less, 0.1% to 10% or less, 1% to 10% or less, 5% to 10% or less, or 7% to 10% or less.

[0042] The porosity of the first porous layer can be achieved depending on the composition of the first porous layer, which will be described later. When the porosity of the first porous layer is 10% or less, a dense structure is formed between the ion-conductive polymers, which facilitates ion conduction and enables the realization of excellent battery characteristics.

[0043] If the porosity of the first porous layer exceeds 10%, a relatively loose structure is formed that makes ion conduction difficult, and as the porosity increases, the ability of the inorganic fine particles and binder resin in the porous layer to inhibit electrode penetration may also decrease.

[0044] The porosity can be calculated from the density / ratio of inorganic fine particles in the slurry, the density / ratio of binder, and the measured weight (loading amount) and thickness of the sample.

[0045] Alternatively, the porosity can be calculated by the following Equation 2 using the ratio of the density obtained by measuring the volume and mass of the first porous layer of a sample coated with the composition on an electrode of a certain area to the theoretical density of the solid content of the coating composition.

[0046] [Formula 2] Porosity (%) = {1-(actual density) / (theoretical density)} x 100

[0047] In the lithium secondary battery electrode according to the embodiment, the first porous layer may include an ion-conducting polymer, which provides conductivity to the second porous layer, thereby minimizing performance degradation of the lithium secondary battery according to the embodiment.

[0048] If the first porous layer does not contain an ion-conductive polymer, a problem may occur in that ion conductivity is not ensured between the electrode substrate and the first porous layer.

[0049] The ion-conductive polymer may be a polymer having a heterocyclic aromatic compound as a monomer. The heterocyclic aromatic compound refers to an aromatic compound having a ring structure and containing one or more heteroatoms selected from O, N, Si, and S.

[0050] In this specification, aromaticity can be defined as a property that satisfies Huckels Rule, and a compound can be defined as aromatic when it satisfies all of the following three conditions according to Huckels Rule:

[0051] 1) There must be 4n+2 electrons in complete conjugation through empty p-orbitals, unsaturated bonds, hole electron pairs, etc. 2) The 4n+2 electrons should form a planar isomer and form a ring structure. 3) All atoms of the ring should participate in the conjugation.

[0052] Examples of the heterocyclic aromatic compound include, but are not limited to, thiophene, furan, pyrrole, imidazole, thiazole, oxazole, oxadiazole, triazole, pyridyl group, bipyridine, pyrimidine, triazine, acridine pyridazine, pyrazine, quinoline, quinazoline, quinoxaline, phthalazine, pyridopyrimidine, pyridopyrazine, pyrazinopyrazine, isoquinoline, indole, carbazole, benzoxazole, benzimidazole, benzothiazole, benzocarbazole, benzothiophene, dibenzothiophene, benzofuranyl group, phenanthroline, isoxazole, thiadiazole, phenothiazine, and dibenzofuran. The heterocyclic aromatic compound may be substituted or unsubstituted.

[0053] More specifically, the heterocyclic aromatic compound may include one or more heterocyclic aromatic compounds selected from the group consisting of thiophene, pyrrole, aniline, or derivatives thereof. That is, the ion-conducting polymer may be a polymer including, as a monomer, one or more heterocyclic aromatic compounds selected from the group consisting of thiophene, pyrrole, aniline, or derivatives thereof.

[0054] For example, the ion-conducting polymer may be a polymer containing one or more monomers selected from the group consisting of 3,4-ethylenedioxythiophene (EDOT), pyrrole, aniline, and thiophene.

[0055] The ion-conductive polymer may include one or more ion-conductive polymers selected from the group consisting of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl(meth)acrylate, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyacrylic acid, polyethyl meth(acrylate), and polycaprolactone.

[0056] The ion-conducting polymer may have a weight average molecular weight of 50,000 g / mol or more and 5,000,000 g / mol or less.

[0057] Specifically, the ion-conductive polymer has a molecular weight of 50,000 g / mol or more, 100,000 g / mol or more, 200,000 g / mol or more, 300,000 g / mol or more, 500,000 g / mol or more, 5,000,000 g / mol or less, 4,000,000 g / mol or less, 3,000,000 g / mol or less, 2,000,000 g / mol or less, 1,000,000 g / mol or less, 50,000 g / mol or more and 5,000,000 g / mol or less, 50,000 g / mol or more and 4,000,000 g / mol or less, 50,000 g / mol or more and ... 00g / mol to 3,000,000g / mol, 50,000g / mol to 2,000,000g / mol, 50,000g / mol to 1,000,000g / mol, 100,000g / mol to 5,000,000g / mol, 100 ,000g / mol to 4,000,000g / mol, 100,000g / mol to 3,000,000g / mol, 100,000g / mol to 2,000,000g / mol, 100,000g / mol to 1,000,000g / mol, 200,000g / mol to 5,000,000g / mol, 200,000g / mol to 4,000,000g / mol, 200,000g / mol to 3,000,000g / mol, 200,000g / mol to 2,000,000g / mol l or less, 200,000g / mol to 1,000,000g / mol, 300,000g / mol to 5,000,000g / mol, 300,000g / mol to 4,000,000g / mol, 300,000g / mol to 3,000,000g The polymer may have a weight average molecular weight of 300,000 g / mol or less to 2,000,000 g / mol, 300,000 g / mol or more to 1,000,000 g / mol, 500,000 g / mol or more to 5,000,000 g / mol, 500,000 g / mol or more to 4,000,000 g / mol, 500,000 g / mol or more to 3,000,000 g / mol, 500,000 g / mol or more to 2,000,000 g / mol, or 500,000 g / mol or more to 1,000,000 g / mol.

[0058] If the weight-average molecular weight of the ion-conducting polymer is too small, the viscosity may decrease, increasing binder penetration into the porous electrode surface and increasing interfacial resistance. Also, if the weight-average molecular weight of the ion-conducting polymer is too large, the chain length of the ion-conducting polymer matrix may increase, resulting in poor electrolyte impregnation in both the amorphous and crystalline regions and reduced ionic conductivity.

[0059] The ion-conducting polymer may have a dielectric constant of 2 or more and 12 or less.

[0060] Specifically, the ion-conducting polymer may have a dielectric constant of 2 or more, 4 or more, 12 or less, 10 or less, 8 or less, 2 or more and 12 or less, 2 or more and 10 or less, 2 or more and 8 or less, 4 or more and 12 or less, 4 or more and 10 or less, or 4 or more and 8 or less.

[0061] If the dielectric constant of the ion-conducting polymer is too low, the solubility of the lithium salt may be reduced, resulting in a decrease in ion conductivity. If the dielectric constant of the ion-conducting polymer is too high, a technical problem occurs in that the insulating properties are reduced due to the high dielectric constant.

[0062] In the lithium secondary battery electrode according to the embodiment, the first porous layer may contain a lithium salt, which may increase the amorphous region in the ion-conducting polymer, thereby increasing the ion diffusion rate, improving electrolyte impregnation, and increasing ion conductivity.

[0063] The lithium salt acts as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes.

[0064] Specifically, the lithium salt may be one or more lithium salts selected from the group consisting of LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCF, SO, LiCF, SO, LiN(CF, SO), LiN(CF, SO), LiN(SOF) (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, LiTFSi, and LiB(C, O) Preferably, the lithium salt may be one or more lithium salts selected from the group consisting of LiPF, LiFSI, and LiTFSi.

[0065] In one embodiment, the first porous layer may include 5 to 200 parts by weight of the lithium salt relative to 100 parts by weight of the ion-conducting polymer.

[0066] Specifically, the first porous layer contains the lithium salt in an amount of 5 parts by weight or more, 10 parts by weight or more, 20 parts by weight or more, 200 parts by weight or less, 100 parts by weight or less, 70 parts by weight or less, 50 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, 5 parts by weight or more and 200 parts by weight, 5 parts by weight or more and 100 parts by weight, 5 parts by weight or more and 70 parts by weight or less, 5 parts by weight or more and 50 parts by weight or less, 5 parts by weight or more and 30 parts by weight or less, 5 parts by weight or more and 25 parts by weight or less, based on 100 parts by weight of the ion-conductive polymer. parts by weight or less, 10 parts by weight or more and 200 parts by weight or less, 10 parts by weight or more and 100 parts by weight or more and 10 parts by weight or more and 70 parts by weight or less, 10 parts by weight or more and 50 parts by weight or less, 10 parts by weight or more and 30 parts by weight or more, 10 parts by weight or more and 25 parts by weight or less, 20 parts by weight or more and 200 parts by weight or more, 20 parts by weight or more and 100 parts by weight or more, 20 parts by weight or more and 70 parts by weight or less, 20 parts by weight or more and 50 parts by weight or less, 20 parts by weight or more and 30 parts by weight or more, 20 parts by weight or more and 25 parts by weight or less.

[0067] If the first porous layer contains less than 5 parts by weight of the lithium salt with respect to 100 parts by weight of the ion-conducting polymer, the absolute lithium ion concentration decreases, resulting in a technical problem of increased resistance.

[0068] In addition, if the first porous layer contains more than 200 parts by weight of the lithium salt per 100 parts by weight of the ion-conducting polymer, the concentration of the lithium salt increases beyond the dissociation degree of the ion-conducting polymer matrix, hindering ion migration within the ion-conducting polymer and resulting in a technical problem of increased resistance.

[0069] In addition, the first porous layer may further include at least one compound selected from the group consisting of nitrile-based compounds and ether-based compounds in addition to the lithium salt.

[0070] When the first porous layer contains one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds, the ionic conductivity can be improved due to the high dielectric constant of the one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds.

[0071] When the first porous layer contains one or more compounds selected from the group consisting of nitrile compounds and ether compounds in addition to the lithium salt, the lithium salt is dissolved in the one or more compounds selected from the group consisting of nitrile compounds and ether compounds. Specifically, the lithium salt is contained in the one or more compounds selected from the group consisting of nitrile compounds and ether compounds at a concentration of 0.1 M to 2.0 M. The lithium salt contained in this concentration range can provide appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance.

[0072] Specifically, the nitrile-based compound may include one or more nitrile-based compounds selected from the group consisting of succinonitrile, adiponitrile, sebaconitrile, acetonitrile, and propionitrile.

[0073] The ether-based compound may include one or more ether-based compounds selected from the group consisting of dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methylhydrofuran, and tetrahydrofuran.

[0074] In one embodiment, when the first porous layer includes all of the at least one compound selected from the group consisting of nitrile-based compounds and ether-based compounds and the lithium salt, the first porous layer may include 50 parts by weight to 1000 parts by weight of the at least one compound selected from the group consisting of nitrile-based compounds and ether-based compounds and the lithium salt, relative to 100 parts by weight of the ion-conducting polymer.

[0075] Specifically, the first porous layer may contain 50 parts by weight or more, 100 parts by weight or more, 101 parts by weight or more, 200 parts by weight or more, 300 parts by weight or more, 1000 parts by weight or more, 800 parts by weight or less, 500 parts by weight or less, 400 parts by weight or less, 50 parts by weight or more and 1000 parts by weight or less, 100 parts by weight or more and 1000 parts by weight or less, 101 parts by weight or more and 1000 parts by weight or more, 200 parts by weight or more and 1000 parts by weight or less, 300 parts by weight or more and 1000 parts by weight or less, 5 ...0 It may be contained in an amount of from 100 to 800 parts by weight, from 101 to 800 parts by weight, from 200 to 800 parts by weight, from 300 to 800 parts by weight, from 50 to 500 parts by weight, from 100 to 500 parts by weight, from 101 to 500 parts by weight, from 200 to 500 parts by weight, from 300 to 500 parts by weight, from 50 to 400 parts by weight, from 100 to 400 parts by weight, from 101 to 400 parts by weight, from 200 to 400 parts by weight, from 300 to 400 parts by weight.

[0076] When the first porous layer contains less than 50 parts by weight of the lithium salt and one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds per 100 parts by weight of the ion-conductive polymer, the plasticity of the lithium salt and the one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds reduces the effect of increasing the amorphous region of the ion-conductive polymer, and the high dielectric constant of the lithium salt and the one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds reduces the solvation effect of the lithium salt, resulting in increased resistance.

[0077] Furthermore, if the first porous layer contains more than 1,000 parts by weight of one or more compounds selected from the group consisting of nitrile compounds and ether compounds and lithium salts per 100 parts by weight of the ion-conductive polymer, the structural properties of the ion-conductive polymer matrix are reduced, resulting in poor mechanical properties.

[0078] In one embodiment, the first porous layer may include inorganic fine particles in an amount of less than 0.0001 parts by weight based on the total weight of the first porous layer, which means that the first porous layer does not include inorganic fine particles.

[0079] As described above, the first porous layer may have a porosity of 10% or less. If an excessive amount of inorganic fine particles is included during the formation of the porous layer, a large number of pores may be formed due to differences in the bonding strength with other components or the degree of expansion, or the degree of pore formation may vary depending on the components included in the porous layer. In contrast, the first porous layer may have such a low porosity by including a relatively low amount of inorganic fine particles or by using other additional components included in the first porous layer, such as an ion-conductive polymer, as described below.

[0080] In the electrode for a lithium secondary battery according to the embodiment, the first porous layer may further include a binder resin in addition to the ion-conducting polymer, and the adhesive strength of the first porous layer may be improved by including the binder resin in the first porous layer.

[0081] In one embodiment, when the first porous layer includes a binder resin, the first porous layer may include 1 to 50 parts by weight of the binder resin relative to 100 parts by weight of the ion-conductive polymer. By including 1 to 50 parts by weight of the binder resin relative to 100 parts by weight of the ion-conductive polymer, the first porous layer may have a porosity of 10% or less.

[0082] Specifically, the first porous layer may include the binder resin in an amount of 1 part by weight or more, 5 parts by weight or more, 50 parts by weight or less, 30 parts by weight or less, 25 parts by weight or less, or 20 parts by weight or less, or 1 part by weight or more, ...25 parts by weight or less, or 1 part by weight or more, 20 parts by weight or less, or 5 parts by weight or more, 5 parts by weight or more, 30 parts by weight or less, 5 parts by weight or more, 25 parts by weight or less, or 5 parts by weight or more, 20 parts by weight or less, or

[0083] If the first porous layer contains less than 1 part by weight of the binder resin per 100 parts by weight of the ion-conductive polymer, the degree of surface binder exposure decreases, resulting in a decrease in adhesive properties, and therefore a decrease in interfacial adhesion between the porous layer and the electrode, resulting in a decrease in cell characteristics. If the first porous layer contains more than 50 parts by weight of the binder resin per 100 parts by weight of the ion-conductive polymer, the decrease in ionic conductivity of the first porous layer results in an increase in internal resistance of the cell.

[0084] The binder resin of the first porous layer may be any one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl flurane, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, flurane, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyurethane, polyacrylic acid, polyimide, and styrene-butadiene rubber, or a mixture of two or more thereof.

[0085] Meanwhile, the second porous layer may include a binder resin and inorganic fine particles.

[0086] The second porous layer can form micropores and adjust the pore size and porosity by adjusting the size of the inorganic fine particles, the content of the inorganic fine particles, and the content of the binder resin. That is, the second porous layer can have a porosity of 30% or more by including the binder resin and the inorganic fine particles.

[0087] The inorganic fine particles are the main component of the second porous layer, and the empty spaces between the inorganic fine particles serve to form micropores and also to act as a kind of spacer that can maintain the physical shape of the second porous layer.

[0088] The inorganic fine particles may have a particle size of 10 nm to 10 μm, and the particle size of the inorganic fine particles may be determined through a scanning electron microscope (SEM) or transmission electron microscope (TEM) image of a cross section of the second porous layer.

[0089] Specifically, the inorganic fine particles may have a particle size of 10 nm or more, 100 nm or more, 10 μm or less, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, or 500 nm or less, and may include inorganic fine particles of 10 nm or more and 10 μm or less, 10 nm or more and 1 μm or less, 10 nm or more and 900 nm or less, 10 nm or more and 800 nm or less, 10 nm or more and 700 nm or less, 10 nm or more and 500 nm or less.

[0090] If the particle size of the inorganic fine particles is less than 10 nm, dispersibility decreases, making it difficult to control the physical properties of the porous layer. If the particle size exceeds 1 μm, the thickness of the porous layer increases, deteriorating mechanical properties. In addition, the pore size is too large, increasing the likelihood of internal short circuits occurring during battery charge and discharge.

[0091] The inorganic fine particles may have a D50 of 10 nm to 1 μm, where D50 refers to the smallest 50% cumulative particle size by mass among particle sizes measured using a laser diffraction / scattering particle size distribution analyzer.

[0092] Specifically, the inorganic fine particles may have a D50 of 10 nm or more, 100 nm or more, 1 μm or less, 900 nm or less, 800 nm or less, 700 nm or less, or 500 nm or less, or may be 10 nm or more, 1 μm or more, 10 nm or more, 900 nm or less, 10 nm or more, 700 nm or less, 10 nm or more, 500 nm or less, 100 nm or more, 1 μm or more, 100 nm or more, 900 nm or less, 100 nm or more, 800 nm or less, 100 nm or more, 700 nm or less, or 100 nm or more, 500 nm or less.

[0093] If the average particle size (D50) of the inorganic fine particles is less than 10 nm, dispersibility decreases, making it difficult to control the physical properties of the porous layer. If it exceeds 1 μm, the thickness of the porous layer increases, reducing mechanical properties. In addition, the pores are too large, increasing the likelihood of internal short circuits occurring during battery charging and discharging.

[0094] In one embodiment, the inorganic fine particles are not particularly limited as long as they are electrochemically stable. Specifically, the inorganic fine particles are not particularly limited as long as they do not undergo oxidation and / or reduction reactions within the operating voltage range of the battery to which they are applied. In particular, when inorganic fine particles with ion transfer ability are used, the ionic conductivity in the lithium secondary battery can be increased, thereby improving performance. Furthermore, when inorganic particles with a high dielectric constant are used as the inorganic fine particles, they can contribute to increasing the degree of dissociation of electrolyte salt, e.g., lithium salt, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte solution.

[0095] For example, the inorganic fine particles may be alumina (Al2O3), boehmite (AlOOH), aluminum hydroxide (Al(OH)3), silica (SiO2), titania (TiO2), zirconia (ZrO2), zirconium titanate (ZrTiO4), La2O3, Y2O3, SrTiO3, BaTiO3, magnesia (MgO), magnesium hydroxide (Mg(OH)2), aluminosilicate (Al2O5Si), zeolite, LLZO (Li7La3Zr2O 12 ), LATP(Li 1+x Al x Ti 2-x (PO4)3,0 <x<2)、PZT(Pb[Zr x Ti 1-x ]O3, 0≦x≦1).

[0096] The second porous layer may contain 50 to 3000 parts by weight of the inorganic fine particles with respect to 100 parts by weight of the binder resin.

[0097] Specifically, the second porous layer contains the inorganic fine particles in an amount of 50 parts by weight or more, 100 parts by weight or more, 110 parts by weight or more, 300 parts by weight or more, 500 parts by weight or more, 900 parts by weight or more, 3000 parts by weight or less, 2500 parts by weight or less, 2000 parts by weight or less, 1500 parts by weight or less, 1000 parts by weight or less, 50 parts by weight or more, 3000 parts by weight or less, 100 parts by weight or more, based on 100 parts by weight of the binder resin. 3,000 parts by weight or less, 110 parts by weight or more and 3,000 parts by weight or less, 300 parts by weight or more and 3,000 parts by weight or less, 500 parts by weight or more and 3,000 parts by weight or less, 900 parts by weight or more and 3,000 parts by weight or less, 50 parts by weight 100 parts to 2,500 parts by weight, 110 parts to 2,500 parts by weight, 300 parts to 2,500 parts by weight, 500 parts to 2,500 parts by weight, 90 parts by weight to 2,500 parts by weight 0 parts by weight to 2,500 parts by weight, 50 parts to 2,000 parts by weight, 100 parts to 2,000 parts by weight, 110 parts to 2,000 parts by weight, 300 parts to 2,000 parts by weight , 500 parts to 2000 parts by weight, 900 parts to 2000 parts by weight, 50 parts to 1500 parts by weight, 100 parts to 1500 parts by weight, 110 parts to 1500 parts by weight It may contain 300 parts by weight or more and 1500 parts by weight or less, 500 parts by weight or more and 1500 parts by weight or less, 900 parts by weight or more and 1500 parts by weight or less, 50 parts by weight or more and 1000 parts by weight or less, 100 parts by weight or more and 1000 parts by weight or less, 110 parts by weight or more and 1000 parts by weight or less, 300 parts by weight or more and 1000 parts by weight or less, 500 parts by weight or more and 1000 parts by weight or less, 900 parts by weight or more and 1000 parts by weight or less.

[0098] The second porous layer can form micropores and adjust the pore size and porosity by adjusting the size of the inorganic fine particles, the content of the inorganic fine particles, and the content of the binder resin. That is, the second porous layer can have a porosity of 30% or more by including 50 to 3,000 parts by weight of the inorganic fine particles per 100 parts by weight of the binder resin.

[0099] If the second porous layer contains less than 50 parts by weight of the inorganic fine particles per 100 parts by weight of the binder resin, the binder resin content is too high, resulting in a decrease in pore size and porosity due to a decrease in void spaces formed between the inorganic fine particles, thereby degrading final battery performance. Also, if the second porous layer contains more than 3,000 parts by weight of the inorganic fine particles per 100 parts by weight of the binder resin, the binder resin content is too low, resulting in a weakened adhesive strength between the inorganic fine particles, thereby reducing peel resistance and degrading the mechanical properties of the second porous layer.

[0100] In the embodiment, the second porous layer may include a binder resin.

[0101] The binder resin of the second porous layer may be any one selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl flurane, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, flurane, carboxymethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyurethane, polyacrylic acid, polyimide, and styrene-butadiene rubber, or a mixture of two or more thereof.

[0102] In the embodiment, the ratio of the thickness of the first porous layer to the thickness of the second porous layer may be 1:1.1 to 1:20.

[0103] Specifically, in one embodiment, the ratio of the thickness of the first porous layer to the thickness of the second porous layer is 1:1.1 or more, 1:1.5 or more, 1:1.8 or more, 1:2 or more, 1:20 or less, 1:10 or less, 1:8 or less, 1:5 or less, or 1:1.1 or more and 1:20 or less, 1:1.1 or more and 1:10 or less, 1:1.1 or more and 1:8 or less, 1:1.1 or more and 1:5 or less, The ratio may be 1:1.5 or more and 1:20 or less, 1:1.5 or more and 1:10 or less, 1:1.5 or more and 1:8 or less, 1:1.5 or more and 1:5 or less, 1:1.8 or more and 1:20 or less, 1:1.8 or more and 1:10 or less, 1:1.8 or more and 1:8 or less, 1:1.8 or more and 1:5 or less, 1:2 or more and 1:20 or less, 1:2 or more and 1:10 or less, 1:2 or more and 1:8 or less, or 1:2 or more and 1:5 or less.

[0104] When the ratio of the thickness of the first porous layer to the thickness of the second porous layer is less than 1:1.1, the thickness of the second porous layer is too thin, making it difficult to ensure heat resistance due to the inorganic fine particles and adhesion due to the binder resin. When the thickness of the second porous layer is too thick, ion conduction is relatively difficult to achieve when an ion-conductive polymer is used at the same thickness, compared to ion conduction through the pores of the porous layer, resulting in increased resistance.

[0105] In addition, if the ratio of the thickness of the first porous layer to the thickness of the second porous layer exceeds 1:20, the thickness of the first porous layer becomes too thin or the thickness of the second porous layer becomes too thick, resulting in a decrease in the insulating properties and / or resistive properties of the battery.

[0106] In the embodiment, the thickness of the first porous layer and the thickness of the second porous layer are not particularly limited, and may be adjusted to, for example, 0.01 to 100 μm in consideration of the performance of the battery.

[0107] For example, the first porous layer may be 0.1 μm or more and 10 μm or less, and the second porous layer may be 5 μm or more and 30 μm or less.

[0108] More specifically, the first porous layer may have a thickness of 0.1 μm or more, 0.5 μm or more, 1 μm or more, 10 μm or less, 7 μm or less, or 5 μm or less, or may have a thickness of 0.1 μm or more and 10 μm or less, 0.5 μm or more and 10 μm or less, 1 μm or more and 10 μm or less, 0.1 μm or more and 7 μm or less, 0.1 μm or more and 7 μm or less, 0.5 μm or more and 7 μm or less, 1 μm or more and 7 μm or less, 0.1 μm or more and 5 μm or less, 0.5 μm or more and 5 μm or less, or 1 μm or more and 5 μm or less.

[0109] If the thickness of the first porous layer is less than 0.1 μm, it cannot protect the electrode, and if it is more than 10 μm, the ionic conductivity decreases and the overall size increases, resulting in a decrease in output characteristics, energy density, etc.

[0110] Furthermore, the second porous layer may have a thickness of 5 μm or more, 8 μm or more, 10 μm or more, 11 μm or more, 30 μm or less, 25 μm or less, or 20 μm or less, or may have a thickness of 5 μm or more, 30 μm or less, 5 μm or more, 25 μm or less, 5 μm or more, 20 μm or more, 8 μm or more, 30 μm or less, 8 μm or more, 25 μm or less, 8 μm or more, 20 μm or more, 10 μm or more, 30 μm or less, 10 μm or more, 25 μm or less, 10 μm or more, 20 μm or more, 11 μm or more, 30 μm or less, 11 μm or more, 25 μm or less, or 11 μm or more, 20 μm or less.

[0111] If the thickness of the second porous layer is less than 5 μm, it is difficult to ensure a uniform coating thickness during the coating process, and if it exceeds 30 μm, it is difficult to ensure a uniform coating thickness during the drying process after coating, which increases the risk of cracks and other problems.

[0112] According to another embodiment of the present invention, there is provided a method for manufacturing an electrode for a lithium secondary battery, comprising: applying a composition for forming a first porous layer onto an electrode substrate and drying the composition to form a first porous layer on at least one surface of the electrode substrate; and applying a composition for forming a second porous layer, the composition including a binder resin and inorganic fine particles, onto the first porous layer and drying the composition to form a second porous layer, wherein the first porous layer has a porosity of 10% or less, and the second porous layer has a porosity of 30% or more.

[0113] The method for manufacturing an electrode for a lithium secondary battery provides the electrode for a lithium secondary battery according to the above-described embodiment. The electrode substrate, the first porous layer, and the second porous layer include all of the above-described contents.

[0114] In the step of forming a first porous layer on at least one surface of the electrode substrate by coating and drying a composition for forming a first porous layer on the electrode substrate, the composition for forming a first porous layer is coated on at least one surface of the electrode substrate, and then the electrode substrate on which the composition for forming a first porous layer has been coated is dried to remove the first solvent contained in the composition for forming a first porous layer.

[0115] In addition, in the step of forming a second porous layer by applying the composition for forming a second porous layer onto the first porous layer and drying it, the composition for forming a second porous layer is applied to one surface of the first porous layer, and then dried to remove the second solvent contained in the composition for forming a second porous layer.

[0116] In the step of forming a first porous layer on at least one surface of the electrode substrate by applying a composition for forming a first porous layer onto the electrode substrate and drying it, and the step of forming a second porous layer by applying a composition for forming a second porous layer, which includes a binder resin and inorganic fine particles, onto the first porous layer and drying it, a conventional coating method well known in the art may be used, such as spin coating, dip coating, die coating, roll coating, comma coating, gravure coating, bar coating, curtain coating, extrusion, casting, screen printing, inkjet printing, doctor blade, or a combination thereof.

[0117] In the method for producing an electrode for a lithium secondary battery, the drying method is not particularly limited and any known method can be used, for example, drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams.

[0118] The solvents used in the first and second porous layer-forming compositions preferably have a solubility index similar to that of the binder resin to be used and a low boiling point to facilitate uniform mixing and subsequent solvent removal. The first solvent is not particularly limited, but may be, for example, one or a mixture of two or more solvents selected from the group consisting of acetone, tetrahydrofuran, methylene chloride, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane.

[0119] Meanwhile, according to another embodiment of the present invention, a lithium secondary battery including the lithium secondary battery electrode can be provided.

[0120] Specifically, according to another embodiment of the present invention, there is provided a lithium secondary battery including the lithium secondary battery electrode, a counter electrode, and an electrolyte interposed therebetween.

[0121] The electrode for a lithium secondary battery includes all of the above.

[0122] Specifically, in the embodiment, the lithium secondary battery may include an electrode assembly wound up with a separator interposed between a positive electrode and a negative electrode, and a case that the electrode assembly is built in. The positive electrode, the negative electrode, and the separator may be impregnated with an electrolyte.

[0123] As described above, the lithium secondary battery of the embodiment includes a lithium secondary battery electrode including, as a separator, a first porous layer formed on the electrode substrate and having a porosity of 10% or less, and a second porous layer formed on the first porous layer, including a binder resin and inorganic fine particles, and having a porosity of 30% or more, instead of a porous polymer separator including a porous substrate and a coating layer formed on the porous substrate. This allows the electrode to maintain adhesion even when the electrode expands and contracts, thereby achieving excellent battery life characteristics.

[0124] The lithium secondary battery of the above embodiment does not include a porous polymer separator including a porous substrate and a coating layer formed on the porous substrate, but may further include an adhesive layer for bonding between the first porous layer included in the electrode for the lithium secondary battery of the above embodiment and a counter electrode, such as a positive electrode or a negative electrode.

[0125] The negative electrode may include a negative electrode material including a negative electrode active material, a conductive material, and a binder; and a current collector that supports the negative electrode material.

[0126] The negative electrode active material may include a material capable of reversibly intercalating and deintercalating lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, and a transition metal oxide.

[0127] The material capable of reversibly intercalating and deintercalating lithium ions may be a carbonaceous material such as crystalline carbon, amorphous carbon, or a mixture thereof. Specifically, the carbonaceous material may be natural graphite, artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitches, mesophase pitch-based carbon fiber, carbon microbeads, petroleum or coal tar pitch-derived cokes, soft carbon, or hard carbon.

[0128] The lithium metal alloy may be an alloy of lithium and a metal containing one or more metals selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, Sn, Bi, Ga, and Cd.

[0129] The substances that can be doped and undoped with lithium may be Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (where Q is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof; provided that Si is excluded), Sn, SnO2, Sn-R alloy (where R is an element selected from the group consisting of alkali metals, alkaline earth metals, group 13 elements, group 14 elements, group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof; provided that Sn is excluded), etc. And as the substances that can be doped and undoped with lithium, at least one of the above examples and SiO2 can be mixed and used. The Q and R may be Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, etc.

[0130] And the transition metal oxide may be vanadium oxide, lithium vanadium oxide, lithium titanium oxide, etc.

[0131] The negative electrode current collector is generally made to have a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it does not induce a chemical change in the battery and has conductivity, and for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those surface-treated with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. can be used. Also, similar to the positive electrode current collector, fine irregularities may be formed on the surface to strengthen the binding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams, non-woven fabric bodies, etc.

[0132] Preferably, the negative electrode can include a negative electrode active material containing one or more selected from the group consisting of a carbonaceous material and a silicon compound.

[0133] Here, the carbonaceous material is a material containing one or more selected from the group consisting of natural graphite, artificial graphite, kish graphite, pyrolytic carbon, mesophase pitch, mesophase pitch-based carbon fiber, carbon microspheres, petroleum or coal-based coke, softened carbon, and hardened carbon, as exemplified above. And the silicon compound may be a compound containing Si exemplified above, that is, Si, Si-C composite, SiOx (0 < x < 2), the Si-Q alloy, a mixture thereof, or a mixture of at least one of these and SiO2.

[0134] Also, the negative electrode can contain micro-silicon. When the negative electrode contains micro-silicon, a capacity superior to that when a carbonaceous material is used as the negative electrode active material can be realized. Specifically, in the case of using specific micro-silicon in the silicon compound, a residual capacity of 80% or more can be maintained even after 500 or more charge and discharge cycles, and an energy density significantly superior to that of a conventional lithium secondary battery can be realized. Further, when the negative electrode contains micro-silicon, the charge-discharge life of a solid battery using a solid electrolyte can be greatly increased, and the charging rate at room temperature can also be greatly improved.

[0135] The size of the micro-silicon is not limited. For example, the micro-silicon can have a diameter of 100 μm or less, or a diameter of 1 to 100 μm, or a diameter of 1 to 20 μm.

[0136] According to one embodiment, the negative electrode active material is contained in an amount of 85% to 98% by weight based on the total weight of the negative electrode material.

[0137] Specifically, the content of the negative electrode active material may be 85% by weight or more, or 87% by weight or more, or 90% by weight or more; and 98% by weight or less, or 97% by weight or less, or 96% by weight or less based on the total weight of the negative electrode material.

[0138] Preferably, the content of the negative electrode active material may be 85% by weight to 98% by weight, 87% by weight to 98% by weight, 90% by weight to 98% by weight, 85% by weight to 97% by weight, 87% by weight to 97% by weight, 90% by weight to 97% by weight, 85% by weight to 96% by weight, 87% by weight to 96% by weight, or 90% by weight to 96% by weight, relative to the total weight of the negative electrode material.

[0139] The conductive material is used to impart electrical conductivity to the electrode.

[0140] The conductive material can be any material that has electronic conductivity without causing chemical changes in the battery. Non-limiting examples of the conductive material include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, samar black, and carbon fiber; graphite, such as natural graphite and artificial graphite; metal powder or metal fiber, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive polymers, such as polyphenylene derivatives. The conductive material can be one or a mixture of two or more of the above examples.

[0141] The content of the conductive material can be adjusted within a range that provides an appropriate level of conductivity without causing a decrease in battery capacity, and is preferably 0.5 wt % to 10 wt %, or 1 wt % to 10 wt %, or 1 wt % to 5 wt %, based on the total weight of the negative electrode material.

[0142] The binder is used to make the negative electrode material adhere well to the current collector.

[0143] Non-limiting examples of the binder include polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc. The binder may be one of the above examples or a mixture of two or more of them.

[0144] The content of the binder is adjusted within a range that provides an appropriate level of adhesiveness without causing a decrease in battery capacity, and is preferably 0.5 wt % to 10 wt %, or 1 wt % to 10 wt %, or 1 wt % to 5 wt %, based on the total weight of the negative electrode material.

[0145] The separator separates the positive electrode and the negative electrode and provides a path for lithium ions to move, and in one embodiment, the first porous layer and the second porous layer may function as the separator. In one embodiment, the first porous layer and the second porous layer may be formed directly on the negative electrode, so that the lithium secondary battery of the one embodiment may include a separator that does not include a porous polymer substrate.

[0146] The lithium secondary battery of the above embodiment may optionally include a porous polymer substrate. The type of the porous polymer substrate is not particularly limited, and may be, for example, polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyaryl ether ketone, polyether imide, or the like. The polymer substrate may be formed of one or more polymers selected from the group consisting of polyetherimide, polyamideimide, polybenzimidazole, polyethersulfone, polyphenyleneoxide, cyclic olefin copolymer, polyphenylenesulfide, and polyethylenenaphthalene, or a mixture of two or more of these polymers, or a multilayer film, woven fabric, or nonwoven fabric thereof.

[0147] The porous polymer substrate may be adjusted in terms of the type and thickness of the substrate, the size and number of pores, and, in the case of a nonwoven fabric, the thickness of the ultrafine threads, taking into consideration the melting temperature, ease of manufacture, porosity, ion migration, insulating properties, etc.

[0148] In the embodiment, the thickness of the porous polymer substrate is not particularly limited and may be adjusted to, for example, 0.01 to 100 μm in consideration of the battery performance.

[0149] The positive electrode for the lithium secondary battery may include a positive electrode material including a positive electrode active material, a binder, a conductive material, and a positive electrode additive; and a current collector supporting the positive electrode material.

[0150] The positive electrode additive for a lithium secondary battery has a property of irreversibly releasing lithium during charging and discharging of the lithium secondary battery, and therefore, when included in the positive electrode of the lithium secondary battery, the positive electrode additive for a lithium secondary battery can serve as a sacrificial positive electrode material for prelithiation.

[0151] Specifically, the positive electrode may be prepared by coating a positive electrode mixture on a positive electrode current collector and then drying the mixture. If necessary, a filler may be further added to the mixture.

[0152] Preferably, the positive electrode for the lithium secondary battery comprises a positive electrode material including a positive electrode active material, a conductive material, the sacrificial positive electrode material, and a binder; and a current collector supporting the positive electrode material.

[0153] As the capacity of a battery increases, the ratio of negative electrode active material in the negative electrode must be increased to increase the battery capacity, and the amount of lithium consumed in the SEI layer also increases. Therefore, after calculating the amount of lithium consumed in the SEI layer of the negative electrode, the amount of sacrificial positive electrode material to be applied to the positive electrode side can be calculated to determine the design capacity of the battery.

[0154] According to one embodiment, the sacrificial cathode material is included in an amount of more than 0 wt % and not more than 15 wt % based on the total weight of the cathode material.

[0155] In order to compensate for irreversible lithium consumed in forming the SEI layer, the content of the sacrificial cathode material is preferably more than 0 wt % with respect to the total weight of the cathode material.

[0156] However, if the sacrificial cathode material is included in an excessive amount, the content of the cathode active material, which exhibits reversible charge / discharge capacity, decreases, resulting in a decrease in battery capacity, and residual lithium in the battery may plate onto the anode, causing a short circuit or impairing safety. Therefore, the content of the sacrificial cathode material is preferably 15 wt % or less of the total weight of the cathode material.

[0157] Specifically, the content of the sacrificial cathode material may be greater than 0 wt %, alternatively 0.5 wt % or more, alternatively 1 wt % or more, alternatively 2 wt % or more, or alternatively 3 wt % or more, based on the total weight of the cathode material; and may be 15 wt % or less, alternatively 12 wt % or less, or alternatively 10 wt % or less.

[0158] Preferably, the content of the sacrificial cathode material may be 0.5% by weight to 15% by weight, alternatively 1% by weight to 15% by weight, alternatively 1% by weight to 12% by weight, alternatively 2% by weight to 12% by weight, alternatively 2% by weight to 10% by weight, or alternatively 3% by weight to 10% by weight, based on the total weight of the cathode material.

[0159] As the positive electrode active material, any compound known in the art to which the present invention pertains to be applicable to lithium secondary batteries can be used without any particular limitation.

[0160] Non-limiting examples of the positive electrode active material include NCM (Li[Ni, Co, Mn]O), NCMA (Li[Ni, Co, Mn, Al]O), LiCoO, LiNiO, LiMnO, LiMnO, and LiNi 1-d Co d O2, LiCo 1-d Mn d O2, LiNi 1-d Mn d O2 (more than, 0≦d<1), Li(NiaCo b Mn c )O4(0 <a<2、0<b<2、0<c<2、a+b+c=2)、LiMn 2-e Ni e O4, LiMn 2-e Co eIt may also be O4 (where 0 < e < 2), LiCoPO4, LiFePO4, etc. As the cathode active material, one or a mixture of two or more of the above examples can be used.

[0161] According to one embodiment, the cathode active material is contained in the total weight of the cathode material at 80% to 98% by weight.

[0162] Specifically, the content of the cathode active material may be 80% by weight or more, or 85% by weight or more, or 90% by weight or more, or 95% by weight or more based on the total weight of the cathode material; and may be 98% by weight or less.

[0163] Preferably, the content of the cathode active material may be 80% to 98% by weight, or 85% to 98% by weight, or 90% to 98% by weight based on the total weight of the cathode material.

[0164] The cathode for the lithium secondary battery can be formed by laminating a cathode material containing the cathode active material, the conductive material, the sacrificial cathode material, and a binder on the current collector.

[0165] The filler is selectively used as a component to suppress the expansion of the cathode, does not induce a chemical change in the battery, and is not particularly limited if it is a fibrous material. For example, olefin polymers such as polyethylene and polypropylene; fibrous substances such as glass fiber and carbon fiber are used.

[0166] The above-mentioned contents are all included for the conductive material and the binder contained in the cathode material and the current collector.

[0167] On the other hand, as the electrolyte, any known electrolyte applicable to lithium secondary batteries in the technical field to which the present invention belongs can be used without particular limitation. For example, the electrolyte may be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, a molten inorganic electrolyte, an aqueous electrolyte, etc.

[0168] The aqueous electrolyte is a salt dissolved in an aqueous solvent such as water or alcohol, and lithium secondary batteries using such an aqueous electrolyte are advantageous in terms of high ionic conductivity and safety, as well as low process and manufacturing costs. Furthermore, batteries using aqueous electrolytes are more environmentally friendly than non-aqueous organic electrolytes.

[0169] Specifically, the electrolyte may be an aqueous electrolyte containing an aqueous solvent and a lithium salt.

[0170] The aqueous solvent is a solvent containing water, and is not particularly limited, but may contain 1 wt % or more of water based on the total weight of the aqueous solvent constituting the electrolyte. The aqueous solvent may be water alone or may be used in combination with a water-miscible solvent.

[0171] The water-miscible solvent may be a polar solvent, and may include, for example, one or more selected from the group consisting of alcohols having 1 to 5 carbon atoms and glycol ethers having 1 to 10 carbon atoms.

[0172] For example, the alcohol having 1 to 5 carbon atoms is one or more selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, glycerol, and 1,2,4-butanetriol, but is not limited thereto.

[0173] The glycol ether having 1 to 10 carbon atoms is at least one selected from the group consisting of ethylene glycol monomethyl ether (MG), diethylene glycol monomethyl ether (MDG), triethylene glycol monomethyl ether (MTG), polyethylene glycol monomethyl ether (MPG), ethylene glycol monoethyl ether (EG), diethylene glycol monoethyl ether (EDG), ethylene glycol monobutyl ether (BG), diethylene glycol monobutyl ether (BDG), triethylene glycol monobutyl ether (BTG), propylene glycol monomethyl ether (MFG), and dipropylene glycol monomethyl ether (MFDG), but is not limited to these.

[0174] The lithium salt contained in the electrolyte dissolves in the aqueous solvent and acts as a lithium ion supply source within the battery, enabling basic operation of the lithium secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0175] Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiN(SO2F)2 (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, and LiB(C2O4)2, etc.

[0176] Preferably, the lithium salt may be LiPF6, LiFSI, and mixtures thereof.

[0177] The lithium salt is contained in the electrolyte at a concentration of 0.1M to 2.0M.

[0178] The lithium salt contained in the above concentration range provides the electrolyte with suitable conductivity and viscosity, thereby enabling the electrolyte to exhibit excellent electrolyte performance.

[0179] Alternatively, the electrolyte can include a non-aqueous organic solvent and a lithium salt.

[0180] The non-aqueous organic solvent may be any solvent that acts as a medium through which ions involved in the electrochemical reaction of the battery can move.

[0181] Specifically, the non-aqueous organic solvent may be an ester-based solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, or ε-caprolactone; an ether-based solvent such as dibutylether or tetrahydrofuran; a ketone-based solvent such as cyclohexanone; an aromatic hydrocarbon-based solvent such as benzene or fluorobenzene; or a dimethylcarbonate (DMC), diethylcarbonate (DMC), or a methylcarbonate (DMCO). Examples of suitable solvents include carbonate solvents such as ethylene carbonate (EC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, which may contain a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolane.

[0182] Among the above examples, carbonate-based solvents can be preferably used as the non-aqueous organic solvent.

[0183] In particular, in consideration of the charge / discharge performance of the battery and compatibility with the sacrificial cathode material, a mixture of a cyclic carbonate (e.g., ethylene carbonate, propylene carbonate) having high ionic conductivity and a high dielectric constant and a linear carbonate (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate) having a low viscosity can be preferably used as the nonaqueous organic solvent. In this case, mixing the cyclic carbonate and the linear carbonate in a volume ratio of 1:1 to 1:9 is advantageous for achieving the above-mentioned performance.

[0184] Furthermore, as the non-aqueous organic solvent, a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:2 to 1:10; or a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of 1-3:1 to 9:1 can be preferably used.

[0185] The lithium salt contained in the electrolyte dissolves in the non-aqueous organic solvent and acts as a source of lithium ions in the battery, enabling basic operation of the lithium secondary battery and promoting the movement of lithium ions between the positive electrode and the negative electrode.

[0186] Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCFSO, LiC4F9SO, LiN(C2F5SO3), LiN(C2F5SO2), LiN(CF3SO2), LiN(SO2F)2 (LiFSI, lithium bis(fluorosulfonyl)imide), LiCl, LiI, LiB(C2O4), etc. Preferably, the lithium salt may be LiPF, LiFSI, or a mixture thereof.

[0187] The lithium salt is contained in the electrolyte at a concentration of 0.1 M to 2.0 M. The lithium salt contained in this concentration range provides the electrolyte with appropriate conductivity and viscosity, thereby enabling the electrolyte to exhibit excellent electrolyte performance.

[0188] Optionally, the electrolyte may contain additives for the purposes of improving the life characteristics of the battery, suppressing the decrease in battery capacity, and improving the discharge capacity of the battery.

[0189] For example, the additive may be a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. The additive is contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0190] The lithium secondary battery of the embodiment may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery, depending on the type of electrolyte and / or the type of separator.

[0191] The liquid electrolyte may be a lithium salt-containing nonaqueous electrolyte, which is composed of a nonaqueous electrolyte and lithium, and the nonaqueous electrolyte may be, but is not limited to, a nonaqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte.

[0192] Examples of organic solid electrolytes that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing ionic dissociative groups.

[0193] Examples of inorganic solid electrolytes that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNI, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0194] In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the lithium salt-containing nonaqueous electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added to impart nonflammability, and carbon dioxide may be further added to improve high-temperature storage properties, or FEC (fluoro-ethylene carbonate), PRS (propene sultone), etc.

[0195] In one specific example, a lithium salt such as LiPF, LiClO, LiBF, or LiN(SOCF) can be added to a mixed solvent of a high dielectric constant solvent, such as a cyclic carbonate (EC) or PC, and a low viscosity solvent, such as a linear carbonate (DEC, DMC, or EMC), to prepare a lithium salt-containing non-aqueous electrolyte.

[0196] The lithium secondary battery is used as an energy source with improved performance and safety in the fields of portable electronic devices such as mobile phones, notebook computers, tablet computers, mobile batteries, and digital cameras; and in the field of transportation means such as electric cars, electric motorcycles, and personal mobility devices.

[0197] The lithium secondary battery may have various shapes such as a prismatic shape, a cylindrical shape, a pouch shape, and the like.

[0198] The lithium secondary battery of the above-described other embodiments can be realized as a battery module including the battery as a unit cell, a battery pack including the battery module, and a device including the battery pack as a power source.

[0199] In this case, specific examples of the device may be, but are not limited to, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

[0200] In the above embodiment, the composition for forming a second porous layer is applied to the first porous layer and dried to form a second porous layer; and after the first and second porous layers are coated, they are assembled through a process such as winding or stacking or lamination, and an electrolyte solution is injected to manufacture a lithium secondary battery. [Effects of the Invention]

[0201] According to the present invention, it is possible to provide an electrode for a lithium secondary battery that can achieve high insulating properties and low resistance properties, a method for manufacturing an electrode for a lithium secondary battery, and a lithium secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0202] The functions and effects of the present invention will be explained in more detail below with reference to specific examples of the present invention, however, these are presented as examples of the present invention and do not limit the scope of the invention in any way.

[0203] Example 1 (1) Manufacturing of the negative electrode 1) Manufacturing of negative electrode substrate Anode active materials (carbon and silicon powders), conductive materials (carbon black), binders (styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC)) were mixed at 95.5 wt%, 1 wt%, 2.5 wt%, and 1 wt%, respectively, and added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare anode slurry. The anode slurry was applied to a 10 μm-thick copper (Cu) thin film anode current collector, dried, and roll-pressed to prepare anode substrates.

[0204] 2) Formation of the first porous layer A composition for forming a first porous layer was prepared by adding ion-conductive polymer polyethylene oxide (weight average molecular weight: 100,000 g / mol to 1,000,000 g / mol, dielectric constant: 5 to 810 g, 2 g of LiTFSi and 30 g of succinonitrile to acetonitrile and dissolving the mixture at 50°C for about 12 hours or more.

[0205] The composition for forming the first porous layer was coated on the prepared negative electrode using a bar coating method under a humidity of 30% and dried at 70°C to form a first porous layer (porosity: 8%) having a thickness of 2 μm.

[0206] 3) Formation of the second porous layer A binder polymer solution was prepared by adding 3 g of polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP) and 7 g of polyetherimide (PEI) to 170 g of N-methyl-2-pyrrolidone (NMP) and dissolving at 50°C for at least 12 hours. 90 g of alumina powder (D50: 500 nm) (30 wt% solids) was added to the prepared polymer solution and crushed and dispersed to 300 nm using a ball mill for at least 12 hours to prepare a composition for forming a second porous layer.

[0207] The composition for forming the second porous layer was coated on the first porous layer by bar coating under a humidity of 30% and dried at 100°C to form a second porous layer (porosity: 60%) having a thickness of 20 μm.

[0208] (2) Manufacturing of the positive electrode A positive electrode slurry was prepared by adding 97.5 wt% of a lithium nickel cobalt manganese aluminum compound as a positive electrode active material, 1 wt% of carbon black as a conductive material, and 1.5 wt% of PVDF as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode slurry was applied to a 10 μm-thick aluminum (Al) thin film positive electrode current collector and dried to prepare a positive electrode, which was then roll-pressed.

[0209] (3)Battery manufacturing The negative electrode having the first and second porous layers formed thereon and the positive electrode were assembled using a stacking method, and an electrolyte (ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 (volume ratio)) and lithium hexachlorophosphate (LiPF 61 mol) were injected into the assembled battery to manufacture a lithium secondary battery.

[0210] Example 2 A lithium secondary battery was manufactured in the same manner as in Example 1, except that succinonitrile was not added when preparing the composition for forming the first porous layer.

[0211] Example 3 A lithium secondary battery was manufactured in the same manner as in Example 2, except that 10 g of polyvinylidene fluoride (weight average molecular weight: 500,000 g / mol to 1,000,000 g / mol, dielectric constant: 4 to 8) was added instead of polyethylene oxide when preparing the composition for forming the first porous layer.

[0212] Example 4 A lithium secondary battery was manufactured in the same manner as in Example 3, except that the lithium salt (LiTFSi) was not added when preparing the composition for forming the first porous layer.

[0213] Comparative Example 1 A lithium secondary battery was fabricated in the same manner as in Example 1, except that the negative electrode having the second porous layer without the first porous layer was assembled with the positive electrode by stacking.

[0214] <Experimental Example> Experimental Example 1: Porous Layer Analysis The thickness and porosity of the first and second porous layers of the lithium secondary batteries fabricated in the Examples and Comparative Examples were analyzed and are shown in Table 1 below.

[0215] The porosity of the porous layer was calculated using the ratio of the actual density of the porous layer to the theoretical density of the solid content of the coating composition according to the following Equation 2.

[0216] [Formula 2] Porosity (%) = {1-(actual density) / (theoretical density)} x 100.

[0217] [Table 1]

[0218] As shown in Table 1, the first porous layer formed in the lithium secondary battery of the example had a thickness of 1 μm to 3 μm and a porosity of 1% or less. Also, the second porous layer formed in the lithium secondary battery of the example had a thickness of 13 μm to 15 μm and a porosity of 30% to 50%.

[0219] Experimental example 2: Dielectric breakdown strength For the negative electrodes of the lithium secondary batteries prepared in the Examples and Comparative Examples, the maximum allowable voltage before dielectric breakdown occurred was measured using a Hi-pot tester at a voltage increase rate of 100 V / sec. The measured maximum voltage was divided by the thickness of the coating film to calculate the maximum allowable voltage per unit thickness, which is shown in Table 2 below.

[0220] Experimental Example 3: EIS Resistor (Lithium Ion Resistor) The lithium secondary batteries manufactured in the examples and comparative examples were subjected to an AC voltage with an amplitude of 10 mV and a frequency of 10 4 ~10 5 The lithium ion resistance was measured by Nyquist plot method using electrochemical impedance spectroscopy (EIS) under 100 Hz conditions, and the results are shown in Table 2 below.

[0221] Experimental Example 4: Peel strength For the lithium secondary batteries of the Examples and Comparative Examples, adhesive tape was attached to the top of the first porous layer and bent 180 degrees to measure the peel strength between the first porous layer and the negative electrode substrate. The results are shown in Table 2 below.

[0222] Experimental Example 5: Battery characteristics The lithium secondary batteries of the Examples, Comparative Examples, and Reference Examples were cycled at room temperature at a 0.1 C-rate between 2.5 and 4.2 V. Additionally, the charge capacity, discharge capacity, and average discharge voltage after repeated cycling were measured according to the capacity retention rate of the materials for 5 cycles, and are shown in Table 3 below.

[0223] [Table 2]

[0224] [Table 3]

[0225] As shown in Tables 2 and 3, the lithium secondary battery of Example 1 includes a first porous layer containing a nitrile compound and having a porosity of 1% or less, which induces uniform distribution of the ionic lithium salt, resulting in a dielectric breakdown strength of 0.45 kV / mil, demonstrating excellent insulation. Furthermore, the lithium secondary batteries of Examples 1 to 4 include a first porous layer and a second porous layer, which results in excellent insulation, and do not experience a charge capacity delay due to voltage increase during one cycle charge. The coulombic efficiency was measured to be high at 76.6% to 80.1%, demonstrating an improved insulation effect.

[0226] In addition, the lithium secondary battery of the embodiment includes the first porous layer and the second porous layer, thereby realizing excellent electrode substrate adhesion and insulating properties, and not only improving the Coulomb efficiency and charge retention rate, but also showing a small increase in resistance, thereby ensuring excellent charge / discharge capacity retention rate.

[0227] On the other hand, in the case of the comparative example, the charge capacity retention rate after 5 cycles was only 80.5%, and it was confirmed that the long-term life characteristics were insufficient.

Claims

1. Electrode base material; a first porous layer formed on the electrode substrate and having a porosity of 0.1% or more and 10% or less; and a second porous layer formed on the first porous layer, comprising a binder resin and inorganic fine particles, and having a porosity of 30% or more; the first porous layer is 0.5 μm or more and 10 μm or less; The inorganic fine particles have a D50 of 10 nm or more and 1 μm or less.

2. The electrode for a lithium secondary battery according to claim 1 , wherein the difference in porosity between the first porous layer and the second porous layer is 20% or more.

3. The electrode for a lithium secondary battery according to claim 1 , wherein the second porous layer has a porosity of 30% to 90%.

4. The inorganic fine particles include alumina, boehmite, aluminum hydroxide, silica, titania, zirconia, zirconium titanate, La ２ O ３ , Y ２ O ３ , SrTiO ３ , BaTiO ３ , magnesia, magnesium hydroxide, aluminosilicate, zeolite, LLZO (Li 7 La 3 Zr 2 O 12 ), LATP (Li 1+x Al x Ti 2-x (PO 4 ) 3 , 0<x<2), PZT (Pb[Zr x Ti 1-x ]O 3 , 0≦x≦1), or Pb[Zr x Ti 1-x ]O 3 , 0≦x≦1.

5. The electrode for a lithium secondary battery according to claim 1 , wherein the second porous layer comprises 50 to 3000 parts by weight of the inorganic fine particles relative to 100 parts by weight of the binder resin.

6. The electrode for a lithium secondary battery according to claim 1 , wherein the first porous layer comprises an ion-conducting polymer.

7. 7. The electrode for a lithium secondary battery according to claim 6, wherein the ion-conducting polymer comprises one or more ion-conducting polymers selected from the group consisting of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl(meth)acrylate, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, and polyethyl meth(acrylate).

8. The electrode for a lithium secondary battery according to claim 6 , wherein the first porous layer contains a lithium salt.

9. The electrode for a lithium secondary battery according to claim 8 , wherein the first porous layer contains 5 to 200 parts by weight of the lithium salt relative to 100 parts by weight of the ion-conducting polymer.

10. 9. The electrode for a lithium secondary battery according to claim 8, wherein the first porous layer comprises at least one compound selected from the group consisting of nitrile-based compounds and ether-based compounds.

11. 11. The electrode for a lithium secondary battery according to claim 10, wherein the first porous layer comprises 50 parts by weight or more and 1000 parts by weight or less of the one or more compounds selected from the group consisting of nitrile-based compounds and ether-based compounds and the lithium salt, relative to 100 parts by weight of the ion-conducting polymer.

12. The electrode for a lithium secondary battery according to claim 1 , wherein the first porous layer comprises inorganic fine particles in an amount of less than 0.0001 parts by weight based on the total weight of the first porous layer.

13. 2. The electrode for a lithium secondary battery according to claim 1, wherein the binder resin comprises one or more binder resins selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl flurane, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, flurane, carboxylmethyl cellulose, acrylonitrile-styrene-butadiene copolymer, polyurethane, polyacrylic acid, polyimide, and styrene-butadiene rubber.

14. 2. The electrode for a lithium secondary battery according to claim 1, wherein a ratio of the thickness of the first porous layer to the thickness of the second porous layer is 1:1.1 to 1:

20.

15. An electrode for a lithium secondary battery as described in claim 1, wherein the second porous layer is 5 μm or more and 30 μm or less.

16. A step of applying a composition for forming a first porous layer onto an electrode substrate and drying the composition to form a first porous layer on at least one surface of the electrode substrate; and forming a second porous layer by applying a composition for forming a second porous layer, the composition including a binder resin and inorganic fine particles, onto the first porous layer and drying the composition; the first porous layer has a porosity of 0.1% or more and 10% or less; the second porous layer has a porosity of 30% or more; the first porous layer is 0.5 μm or more and 10 μm or less; The method for producing an electrode for a lithium secondary battery, wherein the inorganic fine particles have a D50 of 10 nm or more and 1 μm or less.

17. A lithium secondary battery comprising the electrode for a lithium secondary battery according to any one of claims 1 to 15.

Images