Electrode, method for manufacturing electrode, and lithium secondary battery including said electrode

Abstract

The present invention relates to an electrode comprising an electrode current collector and an electrode active material layer disposed on at least one surface of the electrode current collector, the electrode active material layer including an electrode active material and a gel polymer electrolyte, and having an electrode rigidity of 2 kPa to 4 kPa. The present invention also relates to a method for manufacturing an electrode, the method comprising the steps of coating an electrode current collector with an electrode slurry containing an electrolyte solution, placing an oxygen barrier member on the coated electrode slurry, and hot-rolling the electrode slurry covered with the oxygen barrier member, wherein the electrolyte solution is thermally cured by the hot-rolling.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0109522, filed on August 30, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an electrode, a method for producing the electrode, and a lithium secondary battery including the electrode. [Background technology]

[0003] With the increasing technological development and demand for electric vehicles and energy storage systems (ESS), the demand for batteries as their energy source is rapidly increasing. Accordingly, various researches are being conducted on batteries that can meet various requirements. In particular, active researches are being conducted on lithium secondary batteries that have high energy density, excellent life and cycle characteristics as a power source for such devices.

[0004] Generally, a lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. Conventionally, a liquid electrolyte, in which a lithium salt is dissolved in a non-aqueous organic solvent, has been used as an electrolyte for a lithium secondary battery. However, when a liquid electrolyte is used, not only is there a high possibility that the electrode material may degrade and the organic solvent may volatilize, but there is also a risk of combustion or explosion due to an increase in the ambient temperature and the temperature of the battery itself, and there is a risk of leakage, resulting in low safety.

[0005] In recent years, research into various materials and types of solid electrolytes has been actively conducted to overcome the safety issues of liquid electrolytes. Among them, gel electrolytes have the advantage of not only being stable and easy to process, but also having excellent interfacial stability between the electrode and electrolyte due to the inherent adhesive strength of the gel.

[0006] Meanwhile, gel electrolytes can be manufactured by gelling (crosslinking) a mixture of a lithium salt, a solvent, a polymerizable monomer, and an initiator at an appropriate temperature and time. However, if the electrolyte is gelled in an oxygen-containing environment, the gel electrolyte will not harden completely. Furthermore, it takes a considerable amount of time for the gel electrolyte to be impregnated into the electrodes. This can lead to problems such as the gel electrolyte volatilizing during the cell fabrication process or being detached when it comes into contact with other electrodes. To address this issue, gelling the electrolyte in an oxygen-free environment (e.g., a glove box) presents a problem: it is difficult to manufacture large-area all-solid-state batteries due to space limitations.

[0007] This has led to a demand for technological development related to a method for manufacturing large-area all-solid-state batteries by completely impregnating and curing the gel electrolyte even in an oxygen-containing environment. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an electrode that includes an electrode active material layer containing a gel polymer electrolyte and has excellent capacity development characteristics and life performance.

[0009] The present invention aims to provide a method for producing an electrode that overcomes the problems of electrode impregnation with a gel polymer electrolyte and hardening in an oxygen environment, and that has high capacitance development characteristics and excellent electrode rigidity. [Means for solving the problem]

[0010] The present invention provides an electrode comprising an electrode current collector and an electrode active material layer disposed on at least one surface of the electrode current collector, the electrode active material layer comprising an electrode active material and a gel polymer electrolyte, and having an electrode rigidity of 2 kPa to 4 kPa.

[0011] The present invention also provides a method for manufacturing an electrode, the method including the steps of: coating an electrode current collector with an electrode slurry containing an electrolyte; arranging an oxygen barrier member on the coated electrode slurry; and hot-rolling the electrode slurry covered with the oxygen barrier member, wherein the electrolyte is thermally cured by the hot-rolling.

[0012] The present invention also provides a lithium secondary battery comprising the above-described electrode. [Effects of the Invention]

[0013] The electrode according to the present invention is characterized by comprising an electrode active material layer composited with a gel polymer electrolyte, and having an electrode rigidity that satisfies a specific range. The electrode according to the present invention contains a gel polymer electrolyte impregnated into the electrode active material layer, which enables the electrode to exhibit excellent capacity and has high rigidity, thereby realizing a lithium secondary battery with improved output, safety, and life performance.

[0014] Furthermore, according to the electrode manufacturing method of the present invention, unlike conventional techniques in which the electrode is impregnated with the electrolyte after its manufacture, the electrode slurry and the electrolyte solution are mixed together from the beginning to form a gel electrolyte, thereby improving the electrode impregnation property. As a result, problems of lithium deposition and electrolyte volatilization due to non-impregnation of the electrolyte can be solved, and highly volatile electrolyte solutions can be used, thereby broadening the range of electrolyte solutions to choose from. Furthermore, since the electrolyte can be hardened during the electrode manufacturing step, the electrolyte injection and aging processes after cell assembly can be omitted, thereby shortening the cell manufacturing time. Furthermore, according to the electrode manufacturing method of the present invention, the electrolyte solution is hardened while blocking contact between the electrolyte solution and oxygen using an oxygen barrier member, thereby completely hardening the gel electrolyte even in an oxygen-containing environment. As a result, problems such as volatilization of the gel electrolyte during the cell manufacturing process or its detachment due to contact with other electrodes can be prevented. Furthermore, since the electrolyte can be gelled and the electrode can be manufactured even in an oxygen-containing environment, mass production of electrodes is possible through a continuous process using a roll-by-roll system. Furthermore, since there is no need to gel the electrolyte in an oxygen-free environment such as a glove box, large-area electrodes can be manufactured. Meanwhile, the present invention crosslinks the electrolyte solution contained in the electrode slurry using a thermal crosslinking method instead of a UV crosslinking method, thereby allowing the electrolyte solution to be uniformly hardened deep inside the electrode, where UV penetration is difficult. Therefore, when manufacturing a lithium secondary battery, gelation occurs uniformly throughout the electrode without the need to inject a separate liquid electrolyte solution into the electrode laminate or to thin the electrode loading thickness, thereby improving the capacity, output, and life characteristics of the lithium secondary battery. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view for specifically explaining an electrode according to the present invention. [Figure 2] 1 is a graph showing the results of measuring the adhesive strength of the active material layer to the current collector in the negative electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 4. [Figure 3]1 is a graph showing the capacity retention rate as a function of the number of cycles after the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were operated at a temperature of 45° C.; DETAILED DESCRIPTION OF THE INVENTION

[0016] The advantages and features of the present invention, as well as methods for achieving them, will become apparent from the following detailed description of the embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, and may be embodied in a variety of different forms. The present embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art to which the invention pertains. The present invention is defined solely by the scope of the claims. Throughout the specification, the same reference numerals refer to the same elements.

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the sense that they can be commonly understood by a person of ordinary skill in the art to which the present invention belongs. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless they are clearly and specifically defined.

[0018] The terms used in this specification are for the purpose of describing the embodiments and are not intended to limit the present invention. In this specification, the singular includes the plural unless otherwise stated in the text. The words "comprises" and / or "comprising" used in this specification do not exclude the presence or addition of one or more other elements in addition to the elements mentioned.

[0019] In this specification, when a part is said to include a certain component, this means that it may further include other components, not excluding other components, unless otherwise specified to the contrary.

[0020] In this specification, the phrase "A and / or B" means A, or B, or A and B.

[0021] In this specification, "%" means % by weight unless expressly indicated otherwise.

[0022] In this specification, viscosity can be measured using a viscosity measuring device, specifically, a Brookfield viscometer (DV-II+PRO Viscometer, Brookfield) at a temperature of 25°C, a humidity of 50 RH%, and a frequency of 30 Hz.

[0023] <Electrode> The electrode according to the present invention will be described in detail below with reference to Fig. 1. Fig. 1 is a schematic cross-sectional view for specifically explaining the electrode according to the present invention.

[0024] Specifically, the electrode 10 according to the present invention comprises an electrode current collector 110 and an electrode active material layer 120 disposed on at least one surface of the electrode current collector 110, the electrode active material layer 120 comprising an electrode active material and a gel polymer electrolyte, and having an electrode rigidity of 2 kPa to 4 kPa.

[0025] In general, a lithium secondary battery containing a gel polymer electrolyte is manufactured by housing an electrode assembly including electrodes, a separator, etc., in a battery case, injecting a gel polymer electrolyte-forming composition (electrolyte solution) containing a crosslinking material into the battery case, and curing the composition. Lithium secondary batteries manufactured by this method have problems in that it is difficult to improve the desired electrode rigidity due to the presence of unreacted crosslinking material, and it is difficult to sufficiently impregnate the formed gel polymer electrolyte into the interior of the electrode, making it difficult to improve lithium mobility, making it difficult to achieve the desired levels of life performance and output performance.

[0026] To solve these problems, the electrode active material layer 120 is used, in which the gel polymer electrolyte according to the present invention is composited with the electrode active material layer, and the electrode rigidity is adjusted to a specific range. By impregnating and compositing the gel polymer electrolyte, the lithium mobility characteristics in the electrode are improved, making it possible to exhibit capacity, output, and life performance.

[0027] Electrode current collector 110 The electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. Specifically, the electrode current collector may contain at least one material selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and an aluminum-cadmium alloy. For example, if the electrode is a positive electrode, the electrode current collector may contain aluminum, and if the electrode is a negative electrode, the electrode current collector may contain copper.

[0028] The electrode current collector can be used in various forms such as a film, sheet, foil, net, mesh, porous body, foam, nonwoven fabric, etc. The electrode current collector may include a polymer layer and metal layers disposed on both sides of the polymer layer, and the metal layers may include at least one selected from the group consisting of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, and aluminum-cadmium alloy.

[0029] Electrode active material layer 120 The electrode active material layer 120 may be disposed on at least one surface of the electrode current collector. Specifically, the electrode active material layer 120 may be disposed on one or both surfaces of the electrode current collector.

[0030] The electrode active material layer 120 includes an electrode active material and a gel polymer electrolyte. Specifically, the electrode active material layer 120 may be a gel polymer electrolyte composite electrode active material layer in which the electrode active material and the gel polymer electrolyte are composited. Specifically, the gel polymer electrolyte may be impregnated into the electrode active material layer 120. The gel polymer electrolyte may be disposed inside the electrode active material layer 120, or inside and on the surface of the electrode active material layer 120.

[0031] The gel polymer electrolyte may be a cured product of an electrolyte solution including a crosslinking material, a lithium salt, and an organic solvent. The electrolyte solution may be a gel polymer electrolyte-forming composition. The electrolyte solution may further include an initiator.

[0032] The crosslinkable substance may include at least one selected from a crosslinkable monomer (hereinafter referred to as a "monomer") and a crosslinkable oligomer (hereinafter referred to as an "oligomer").

[0033] The monomer and / or oligomer is a substance that can form a gel polymer electrolyte by a polymerization reaction.

[0034] The monomer may be, but is not limited to, ethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate (ETPTA), bisphenol A ethoxylated dimethacrylate, acrylic acid, carboxyethyl acrylate, carboxyethyl acrylate, methyl cyanoacrylate, ethyl cyanoacrylate, ethyl cyanoethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, hydroxypropyl acrylate, derivatives thereof, or combinations thereof.

[0035] The oligomer may include at least one selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, acrylate-based oligomers, polysiloxane-based oligomers, phosphazene-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride. Specifically, the oligomer may include at least one selected from the group consisting of fluorine-based oligomers, polycarbonate-based oligomers, and polysiloxane-based oligomers.

[0036] The monomer and / or oligomer may be included in an amount of 4 to 40 parts by weight, specifically 5 to 40 parts by weight, and more specifically 5 to 30 parts by weight, per 100 parts by weight of the electrolyte. If the content of the monomer and / or oligomer is less than 4 parts by weight per 100 parts by weight of the electrolyte, the cross-linking reaction between the monomer and / or oligomer may be insufficient, resulting in a problem of reduced adhesion between the current collector and the electrode active material layer. Furthermore, if the content of the monomer and / or oligomer is more than 40 parts by weight per 100 parts by weight of the electrolyte, the electrode resistance may increase.

[0037] The lithium salt is used as a medium for transferring ions in a lithium secondary battery.

[0038] Lithium salts are substances that are easily dissolved in gel polymer electrolytes, such as LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 The lithium fluoride may include, but is not limited to, a single substance or a mixture of two or more substances selected from the group consisting of LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, LiFSI, LiTFSI, LiB(CO2O4)2, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, and imide.

[0039] The concentration of the lithium salt in the electrolyte may be 0.1 M to 5.0 M, preferably 0.1 M to 3.0 M, and more preferably 0.2 M to 3.0 M. When the lithium salt is contained within the above content range, the cured electrolyte may have sufficient ionic conductivity.

[0040] The organic solvent is for dissolving the aforementioned monomer and / or oligomer, initiator, and lithium salt.

[0041] The organic solvent is one that is commonly used in secondary batteries, and may be, for example, ether, ester (acetates, propionates), amide, linear or cyclic carbonate, nitrile (acetonitrile, SN, etc.), etc., which may be used alone or in combination of two or more.

[0042] Among these, typically, carbonate-based solvents containing carbonate compounds such as cyclic carbonates, linear carbonates, or mixtures thereof may be used.

[0043] Specific examples of the cyclic carbonate compound include a single compound or a mixture of at least two compounds selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, and halides thereof. Specific examples of the linear carbonate compound include a compound or a mixture of at least two compounds selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC), but are not limited thereto.

[0044] In particular, among the carbonate-based solvents, the cyclic carbonates propylene carbonate and ethylene carbonate are preferred because they are high-viscosity organic solvents with high dielectric constants that facilitate dissociation of lithium salts in the electrolyte solution. When such cyclic carbonates are mixed in an appropriate ratio with a linear carbonate having a low viscosity and a low dielectric constant, such as ethyl methyl carbonate, diethyl carbonate, or dimethyl carbonate, an electrolyte solution having high electrical conductivity can be produced, and therefore these cyclic carbonates are more preferred.

[0045] Among the organic solvents, the ester may be a single compound or a mixture of at least two compounds selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, α-valerolactone, and ε-caprolactone, but is not limited thereto.

[0046] The initiator is a substance that forms active radicals to initiate a polymerization reaction of a monomer and / or oligomer. Specifically, the initiator can be decomposed by light such as UV at room temperature (5°C to 30°C) or by heat at 30°C to 100°C to form radicals, thereby initiating a free radical polymerization reaction of a monomer and / or oligomer.

[0047] The initiator may be a thermal cure initiator. For example, the initiator may include at least one selected from the group consisting of benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide, and hydrogen peroxide, 2,2′-azobis(2-cyanobutane), 2,2′-azobis(methylbutyronitrile), 2,2′-azobis(isobutyronitrile) (AIBN), and 2,2′-azobisdimethyl-valeronitrile (AMVN).

[0048] The initiator may be included in an amount of 0.01 to 10 parts by weight, specifically 0.05 to 7 parts by weight, and more specifically 0.06 to 5 parts by weight, based on 100 parts by weight of the monomer and / or oligomer. When the initiator is included in this amount range, the crosslinking reaction between the monomer and / or oligomer proceeds smoothly, ensuring adhesion between the current collector and the electrode active material layer, and controlling the polymerization rate in the electrolyte, thereby preventing the disadvantage of unreacted initiator remaining and adversely affecting battery performance.

[0049] The electrode 10 has an electrode rigidity of 2 kPa to 4 kPa. When the electrode rigidity of the electrode 10 is within this range, it can be understood that the gel polymer electrolyte is sufficiently impregnated into the electrode active material layer 120. When the electrode rigidity of the electrode 10 is less than 2 kPa, it is considered that the impregnation of the gel polymer electrolyte into the electrode active material layer 120 is insufficient, or that unreacted or uncured crosslinking material (e.g., crosslinking monomer, crosslinking oligomer) is present at an unnecessary level. In this case, problems such as a decrease in lithium mobility, difficulty in capacity development, and generation of side reaction gases may occur. When the electrode rigidity of the electrode 10 exceeds 4 kPa, the resistance may be too high, making it difficult to achieve the desired output performance and lifespan. Furthermore, the brittleness of the electrode itself may weaken, leading to problems such as the generation of foreign matter due to cracks at the electrode edge, which may result in an internal short circuit.

[0050] The electrode stiffness can be measured using a universal testing machine (UTM). Specifically, the electrode stiffness refers to the maximum stiffness measured by attaching an electrode to an aluminum (Al) jig with a 5 cm diameter hole and then pressing the electrode with a metal rod with a 2 cm diameter using a UTM device. Because the electrode stiffness is measured by pressing with the metal rod, it is not significantly affected by the area, thickness, loading amount, etc. of the electrode.

[0051] The method for achieving the above-mentioned range of electrode rigidity is not particularly limited, and can be achieved, for example, by using a mixture of an electrode active material and an electrolytic solution (a composition for forming a gel polymer electrolyte) as an electrode slurry used in producing an electrode active material layer, by replacing the binder in the electrode slurry with a gel polymer electrolyte, by producing an electrode active material layer by a hot rolling method using an oxygen-blocking member, by using an electrode production method described below, or the like.

[0052] The electrode may be a positive electrode or a negative electrode.

[0053] When the electrode is a positive electrode, the electrode active material layer may be a positive electrode active material layer, and the electrode active material may be a positive electrode active material.

[0054] The positive electrode active material may be a lithium transition metal oxide, and may be any material that allows easy intercalation and deintercalation of lithium ions during charging and discharging. For example, the positive electrode active material may be one or more selected from a lithium nickel cobalt composite oxide, a lithium manganese composite oxide, and a lithium iron phosphate composite oxide.

[0055] Specifically, the positive electrode active material may include the lithium nickel cobalt-based composite oxide represented by the following Chemical Formula 1:

[0056] [Chemical formula 1] Li 1+x (Ni a Co b Mn c M d )O2

[0057] In the above Chemical Formula 1, M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 1+x, a, b, c, and d are each independently mole ratios of elements; -0.2 ≤ x ≤ 0.2, 0.60 ≤ a < 1, 0 < b ≤ 0.30, 0 < c ≤ 0.30, 0 ≤ d ≤ 0.10, and a + b + c + d = 1.

[0058] The 1 + x represents the molar ratio of lithium in the lithium nickel cobalt composite oxide, and it may be -0.1 ≤ x ≤ 0.2 or 0 ≤ x ≤ 0.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel cobalt composite oxide can be stably formed.

[0059] The a represents the molar ratio of nickel among all the metals excluding lithium in the lithium nickel cobalt composite oxide, and it may be 0.70 ≤ a < 1, 0.75 ≤ a < 1, or 0.80 ≤ a < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0060] The b represents the molar ratio of cobalt among all the metals excluding lithium in the lithium nickel cobalt composite oxide, and it may be 0 < b ≤ 0.20, 0 < b ≤ 0.15, or 0 < b ≤ 0.10. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0061] The c represents the molar ratio of manganese among all the metals excluding lithium in the lithium nickel cobalt composite oxide, and it may be 0 < c ≤ 0.20, 0 < c ≤ 0.15, or 0 < c ≤ 0.10. When the molar ratio of manganese satisfies the above range, it has excellent structural stability of the positive electrode active material.

[0062] In one embodiment of the present invention, the lithium nickel cobalt composite oxide may contain one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo. Preferably, the doping element may be Al. In other words, the d, which represents the molar ratio of the doping element to all metals excluding lithium in the lithium composite transition metal oxide, is 0. <d≦0.10、0<d≦0.08、または0<d≦0.05であってよい。

[0063] Preferably, a, b, c, and d are in the range of 0.70≦a<1, 0 <b≦0.2、0<c≦0.2、0≦d≦0.1であってよい。

[0064] The lithium manganese composite oxide is Li p Mn 1-q M q A2, Li p MnO 4-r X r , Li p Mn 2-q M q M' r A4, Li p Co 1-q M q A2, Li p Co 1-q M q O 2-r X r , Li p Ni 1-q M q O 2-r X r , Li p Ni 1-q Co q O 2-r X r , Li p Ni 1-q-r Co q M r A w , Li p Ni 1-q-r Co q M r O 2-w X w , Li pNi 1-q-r Mn q M r A w , and Li p Ni 1-q-r Mn q M r O 2-w X w wherein p, q, r, and w are 0.9≦p≦1.2, 0≦q≦1, 0≦r≦1, and 0≦w≦2, respectively; M and M′ are the same or different and are one or more elements selected from the group consisting of Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Cr, Fe, Sr, V, and rare earth elements; A is one or more elements selected from the group consisting of O, F, S, and P; and X is one or more elements selected from the group consisting of F, S, and P.

[0065] The lithium iron phosphate composite oxide may be represented by the following chemical formula 2.

[0066] [Chemical formula 2] Life 1-x M x PO4

[0067] In the above Chemical Formula 2, M is one or more selected from Ni, Co, Mn, Al, Mg, Y, Zn, In, Ru, Sn, Sb, Ti, Te, Nb, Mo, Cr, Zr, W, Ir, and V; 0≦x<1.

[0068] The positive electrode active material may be contained in the positive electrode active material layer in an amount of 80% by weight to 99% by weight, specifically 90% by weight to 99% by weight.

[0069] The positive electrode active material layer may further include a conductive material.

[0070] The conductive material is a substance that imparts conductivity to the battery without causing any chemical change, and may be added to the positive electrode active material layer in an amount of 0.5% by weight to 20% by weight.

[0071] The conductive material may be selected from, for example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotubes, and graphite; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0072] The positive electrode active material layer may further include a binder.

[0073] The binder is a component that aids in bonding the active material to the conductive material and the current collector, and is typically added to the positive electrode active material layer in an amount of 1 to 30% by weight. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0074] When the electrode 10 is a positive electrode, the electrode rigidity of the electrode may be 2 kPa to 4 kPa, specifically 2.5 kPa to 3.5 kPa, more specifically 2.75 kPa to 3.25 kPa, and even more specifically 2.75 kPa to 2.85 kPa.

[0075] When the electrode is a negative electrode, the electrode active material layer may be a negative electrode active material layer, and the electrode active material may be a negative electrode active material.

[0076] The negative electrode active material may include one or more selected from a carbonaceous material capable of reversibly intercalating / deintercalating lithium ions; a metal or an alloy of these metals with lithium; a metal composite oxide; a material capable of doping and undoping lithium; lithium metal; and a transition metal oxide, and preferably may be a carbonaceous material.

[0077] As the carbonaceous material capable of reversibly intercalating / deintercalating lithium ions, any carbonaceous negative electrode active material generally used in a lithium ion secondary battery can be used without particular limitation, and representative examples thereof include crystalline carbon, amorphous carbon, or both of them can be used. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon), hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0078] As the metal or an alloy of these metals with lithium, a metal selected from the group consisting of Cu, Ni, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn or an alloy of these metals with lithium can be used.

[0079] Examples of the metal composite oxide include PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, Bi2O5, Li x Fe2O3 (0 ≦ x ≦ 1), Li x WO2 (0 ≦ x ≦ 1), and Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, elements of Group 1, Group 2, Group 3 of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), and one or more selected from the group can be used.

[0080] Examples of the substance capable of doping and undoping lithium include Si, SiO x (0 < x < 2), Si-Y alloy (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Si), Sn, SnO2, Sn-Y (where Y is an element selected from the group consisting of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), etc. Further, at least one of these may be mixed with SiO2 and used. The element Y may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db (dubnium), 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0081] Examples of the transition metal oxide include lithium-containing titanium composite oxide (LTO), vanadium oxide, lithium vanadium oxide, etc.

[0082] The negative electrode active material may be contained in the negative electrode active material layer at 80% to 99% by weight.

[0083] The negative electrode active material layer may further contain a conductive material.

[0084] Further, the conductive material is a substance that imparts conductivity without causing a chemical change to the battery, and may be added to the negative electrode active material layer at 0.5% to 20% by weight.

[0085] The conductive material may be selected from, for example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; graphite powder such as natural graphite, artificial graphite, carbon nanotubes, and graphite; conductive fibers such as carbon fibers and metal fibers; conductive powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0086] The negative electrode active material layer may further include a binder.

[0087] The binder is a component that aids in binding the active material to the conductive material and the current collector, and is typically added to the negative electrode active material layer in an amount of 1 to 30% by weight. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer, sulfonated ethylene-propylene-diene monomer, styrene-butadiene rubber, fluororubber, and various copolymers thereof.

[0088] When the electrode 10 is a negative electrode, the electrode rigidity of the electrode 10 may be 2 kPa to 4 kPa, specifically 2 kPa to 3 kPa, and more specifically 2.1 kPa to 2.7 kPa.

[0089] In the present invention, the electrode active material layer (positive electrode active material layer or negative electrode active material layer) may not contain a binder. As described above, the electrode active material layer of the present invention contains a gel polymer electrolyte or a cured product of an electrolytic solution (gel polymer electrolyte-forming composition), and the gel polymer electrolyte can instead play the role of a binder. Depending on the binder used, the electrode active material layer may have too high rigidity or may act as a detrimental factor to resistance. Therefore, the gel polymer electrolyte functions to bind the electrode active material and / or electrode current collector and can improve lithium mobility.

[0090] The thickness of the electrode 10 or the electrode active material layer 120 may be 50 μm to 1,000 μm, specifically 50 μm to 500 μm, and more specifically 50 μm to 300 μm.

[0091] In the present invention, the electrode 10 may further include a coating layer 130. The coating layer 130 may be disposed on the surface of the electrode 10, specifically, on the surface opposite to the surface where the electrode active material layer 120 and the electrode current collector 110 face each other.

[0092] The coating layer 130 may include a gel polymer electrolyte. Specifically, the coating layer 130 may consist of only a gel polymer electrolyte.

[0093] The gel polymer electrolyte contained in the coating layer 130 may be the same as the gel polymer electrolyte contained in the electrode active material layer 120 .

[0094] The gel polymer electrolyte included in the coating layer 130 refers to a gel polymer electrolyte formed on the surface of the electrode active material layer when the gel polymer electrolyte included in the electrode active material layer is formed.

[0095] <Electrode manufacturing method> The present invention also provides a method for producing an electrode, which may be the method for producing an electrode described above.

[0096] A method for manufacturing an electrode according to the present invention includes the steps of: coating an electrode current collector with an electrode slurry containing an electrolyte solution, disposing an oxygen barrier member on the coated electrode slurry, and hot-rolling the electrode slurry covered with the oxygen barrier member, wherein the electrolyte solution is thermally cured by the hot-rolling. In this case, the electrode manufactured by the method may be a positive electrode or a negative electrode.

[0097] Unlike conventional techniques in which the electrolyte is impregnated after the electrodes are manufactured, the present invention improves the electrode impregnation ability of the electrolyte by gelling the gel electrolyte in a state in which the electrode slurry and the electrolyte solution are mixed from the beginning. As a result, problems of lithium deposition and electrolyte volatilization due to non-impregnation of the electrolyte can be solved, and highly volatile electrolyte solutions can be used, allowing for a wider range of electrolyte solutions to be selected. Furthermore, because the electrolyte can be hardened during the electrode manufacturing step, the electrolyte injection and aging processes after cell assembly can be omitted, thereby shortening the cell manufacturing time.

[0098] According to the present invention, the gel electrolyte can be completely cured even in an oxygen-containing environment by using an oxygen-blocking member to cure the electrolyte while blocking contact between the electrolyte and oxygen. As a result, problems such as volatilization of the gel electrolyte or its detachment due to contact with other electrodes during the cell fabrication process can be prevented. Furthermore, because the gelation of the electrolyte and the manufacture of electrodes can be achieved even in an oxygen-containing environment, mass production of electrodes can be achieved through a continuous process in roll units. Furthermore, because there is no need to gel the electrolyte in a space such as a glove box where an oxygen-free environment is realized, large-area electrodes can be manufactured.

[0099] Meanwhile, the present invention crosslinks the electrolyte solution contained in the electrode slurry using a thermal crosslinking method instead of a UV crosslinking method. This allows the electrolyte solution to be uniformly cured deep inside the electrode, where UV penetration is difficult. Therefore, when manufacturing a lithium secondary battery, gelation occurs uniformly throughout the electrode without the need to inject a separate liquid electrolyte into the electrode laminate or to thin the electrode loading thickness, thereby improving the capacity, output, and life characteristics of the lithium secondary battery.

[0100] (1) A step of coating an electrode current collector with an electrode slurry containing an electrolyte. First, the method for producing an electrode of the present invention begins with a step of coating an electrode current collector with an electrode slurry.

[0101] The coated electrode slurry can be subjected to a hot-rolling process (described below) to form an electrode active material layer. Because the hot-rolling process is performed in the presence of an oxygen barrier, no unreacted crosslinking material remains, allowing a gel polymer electrolyte with a high curing rate to be present in the electrode active material layer. The electrode active material layer produced from the hot-rolling process has an appropriate level of electrode rigidity, enabling the realization of a lithium secondary battery with excellent rigidity and improved capacity development, output performance, and lifespan.

[0102] The electrode current collector has been described above.

[0103] Next, the electrode slurry of the present invention includes an electrolyte solution. In this case, the electrolyte solution may be a composition for forming a gel polymer electrolyte. Specifically, the electrolyte solution may include a crosslinking material, a lithium salt, and an organic solvent. The electrolyte solution may further include an initiator. The details of the electrolyte solution, the crosslinking material, the lithium salt, the organic solvent, and the initiator are as described above.

[0104] The electrode slurry may further include an electrode active material. The electrode active material may be a positive electrode active material or a negative electrode active material. The electrode slurry may further include a conductive material and / or a binder. The electrode active material, conductive material, and binder are as described above.

[0105] On the other hand, the electrode slurry of the present invention may not contain a binder, in which case the binder is a conventional binder used in the manufacture of conventional electrodes, such as polyvinylidene fluoride (PVDF).

[0106] In place of the binder, the thermoset electrolyte polymer in the electrode of the present invention can serve to assist in bonding between the active material and the conductive material, or bonding to the current collector. Since the electrode slurry does not contain a binder, there is an effect of relatively reducing the electrode resistance.

[0107] The electrode slurry of the present invention may be free of any solvent other than the organic solvent of the electrolyte. Specifically, the electrode slurry may be free of N-methyl-2-pyrrolidone (NMP). Conventionally, electrodes have been manufactured by forming an electrode active material layer from an electrode slurry and then impregnating the electrode active material layer with an electrolyte. In this process, a separate drying and rolling process was performed to remove the N-methyl-2-pyrrolidone (NMP) solvent contained in the electrode slurry. However, this rolling process can damage the active material, resulting in reduced battery life. However, the present invention uses a mixture of an active material and a conductive material in the electrolyte, rather than impregnating the electrode active material layer with the electrolyte. This eliminates the drying and rolling processes for forming the active material layer, thereby minimizing damage to the active material.

[0108] The solid content of the electrode slurry may be 30% to 80%, specifically 40% to 80%, more specifically 50% to 80%. When the solid content of the electrolyte satisfies the above numerical range, the electrode contains an appropriate amount of hardened electrolyte, improving electrode processability and optimizing battery performance.

[0109] In addition, when the solid content of the electrolyte solution satisfies the above numerical range, the electrode slurry may have a viscosity at a level that allows it to be coated onto an electrode current collector. For example, the viscosity of the electrode slurry at 25°C may be 20,000 cP or less, specifically 3,000 cP to 15,000 cP, and more specifically 4,000 cP to 12,000 cP.

[0110] The electrode slurry containing the electrolyte may be mixed by a conventional mixing method, for example, by stirring the electrode slurry containing the electrolyte using a homogenizer.

[0111] The electrode slurry containing the electrolyte can be coated by a conventional coating method, such as bar coating, spin coating, roll coating, slot die coating, hand coating, or spray coating. One of these methods can be used alone, or two or more of these methods can be used in combination.

[0112] (2) placing an oxygen barrier member on the coated electrode slurry; Next, an oxygen barrier is placed on the coated electrode slurry. By covering the electrode slurry with the oxygen barrier, it is possible to block contact between the electrolyte solution contained in the electrode slurry and oxygen. Furthermore, if there is no oxygen barrier on the electrode slurry, the electrode slurry may adhere to the rolling member during rolling, resulting in poor processability and inconsistent thickness and loading of the produced electrodes.

[0113] The oxygen barrier member may be insoluble in a solvent so as to effectively block contact between the electrolyte and oxygen. Specifically, the oxygen barrier member may be insoluble in an organic solvent. The oxygen barrier member may also include a flexible material so that it can be wound into a roll together with the electrode.

[0114] For example, the oxygen barrier member may include, but is not limited to, one or more selected from the group consisting of polypropylene (PP) and high density polyethylene (HDPE).

[0115] The thickness of the oxygen-blocking member may be 20 μm to 2000 μm, specifically 50 μm to 500 μm, more specifically 50 μm to 200 μm. When the thickness of the oxygen-blocking member satisfies the above numerical range, contact between the electrolyte and oxygen is blocked, allowing the electrolyte to be completely cured.

[0116] (3) hot-rolling the electrode slurry covered with the oxygen-blocking member; Next, the electrode slurry covered with the oxygen blocking member is hot-rolled, whereby the electrolyte contained in the electrode slurry is thermally hardened.

[0117] Thermal curing of an electrolyte solution involves applying heat to an electrolyte solution covered with an oxygen barrier member to crosslink the crosslinkable substances (monomers and / or oligomers) contained in the electrolyte solution. The electrolyte solution is cured while the oxygen barrier member prevents contact between the electrolyte solution and oxygen, preventing the electrolyte solution from volatilizing or coming into contact with other electrodes and being separated.

[0118] According to the present invention, the hot-rolling step may include rolling the electrode slurry with a rolling roller. By hot-rolling the electrode slurry using the rolling roller, the electrolyte contained in the electrode slurry may be thermally cured.

[0119] The surface temperature of the pressure roller may be 30° C. to 80° C., specifically 40° C. to 80° C., more specifically 50° C. to 70° C. When the surface temperature of the pressure roller satisfies the above range, it is possible to realize temperature conditions that do not damage the oxygen-blocking member and allow the electrolyte to be crosslinked.

[0120] According to the present invention, the electrode loading thickness can be controlled by adjusting the gap between the rolling roller and the electrode slurry. By controlling the electrode loading thickness, the capacity of a lithium secondary battery including the electrode manufactured according to the present invention can be controlled.

[0121] After the hot rolling, the electrolyte impregnated inside the electrode and the electrolyte present on the surface of the electrode may be hardened. In this case, the hot rolling may harden the electrolyte present on the surface of the electrode, thereby forming an electrolyte layer (e.g., coating layer 130 in FIG. 1) on the electrode.

[0122] The electrolyte layer may include a polymer matrix formed by crosslinking a monomer and / or oligomer with an initiator, and a lithium salt impregnated in the polymer matrix. In this case, the electrolyte layer may have ionic conductivity due to the lithium salt.

[0123] The degree of hardening of the electrolyte layer may be 93% to 100%, specifically 95% to 100%, more specifically 98% to 100%. When the degree of hardening of the electrolyte layer satisfies the above range, the electrolyte layer can be formed on the active material layer with a uniform thickness, and the phenomenon of the electrolyte layer being detached from the active material layer can be prevented.

[0124] The thickness of the electrolyte layer may be 1 μm to 200 μm, specifically 5 μm to 150 μm, and more specifically 5 μm to 80 μm. When the thickness of the electrolyte layer satisfies the above numerical range, the electrolyte layer is prevented from being separated from the active material layer, and the cations (Li + ) can easily pass through, minimizing the performance degradation due to the total volume of the lithium secondary battery.

[0125] After the hot rolling, the thickness of the electrode or electrode active material layer may be 50 μm to 1,000 μm, specifically 50 μm to 500 μm, and more specifically 50 μm to 300 μm. If the electrode thickness is less than 50 μm, the electrode loading thickness may not be sufficiently ensured, which may result in a decrease in battery capacity. Furthermore, if the electrode thickness exceeds 1,000 μm, the ion conduction path may be too long, resulting in poor battery output performance, and the electrolyte inside the electrode slurry may not be uniformly hardened because heat does not reach deep inside the electrode slurry.

[0126] (4) heating the electrode after the hot rolling The method for manufacturing an electrode according to the present invention may further include a step of heating the electrode after the hot rolling, which can further thermally harden the electrolyte in the electrode.

[0127] The heating step may include storing the electrode at a temperature of 40° C. to 80° C. for 10 minutes to 24 hours.

[0128] In this case, the temperature may be 40° C. to 80° C., specifically 50° C. to 80° C., more specifically 60° C. to 70° C. Controlling the storage temperature within the above range is preferable from the viewpoint of curing the uncured electrolyte solution in the electrode slurry and maintaining the stability of the remaining components contained in the electrode slurry.

[0129] The storage period may be from 10 minutes to 24 hours, specifically from 1 hour to 10 hours, and more specifically from 1 hour to 5 hours.

[0130] If the battery is stored for less than 10 minutes, the internal temperature of the battery does not rise sufficiently, preventing curing. If the battery is stored for more than 24 hours, certain additives in the battery may decompose.

[0131] The storing step may correspond to storing the electrode roll, in which the current collector / electrode slurry / oxygen barrier member are sequentially stacked and wound, in a high-temperature chamber. This minimizes the evaporation of the electrolyte in the electrode even when a vacuum is applied to the high-temperature chamber. Furthermore, the space in the chamber can be used efficiently, thereby improving electrode productivity.

[0132] A vacuum may be formed in the high-temperature chamber, which removes oxygen from the chamber and allows the electrolyte solution to be cured in a shorter time.

[0133] On the other hand, once the hardening of the electrolyte is complete, the oxygen barrier member disposed on the electrode may be removed.

[0134] <Lithium secondary battery> The present invention also provides a lithium secondary battery comprising the above-described electrode.

[0135] Specifically, the lithium secondary battery may include an electrode assembly including two or more electrodes, and the electrode assembly may be formed by stacking two or more electrodes.

[0136] At least one of the two or more electrodes may be the above-described electrodes. Specifically, all of the two or more electrodes may be the above-described electrodes. The electrode assemblies may each be formed by alternately stacking one or more positive electrodes and one or more negative electrodes, and the positive electrodes and the negative electrodes may be the above-described electrodes. The electrode assemblies may be formed such that a positive electrode active material layer of the positive electrode faces a negative electrode active material layer of the negative electrode, a positive electrode active material layer of the positive electrode faces a coating layer of the negative electrode, a coating layer of the positive electrode faces a negative electrode active material layer of the negative electrode, or a coating layer of the positive electrode faces a coating layer of the negative electrode.

[0137] According to one embodiment of the present invention, the lithium secondary battery of the present invention does not need to include a separator disposed between the positive electrode and the negative electrode as in conventional lithium secondary batteries. Specifically, the electrolyte layer (coating layer) formed on the surface of the electrode of the present invention is disposed between the positive electrode and the negative electrode, thereby fulfilling the role of a conventional separator.

[0138] According to another embodiment of the present invention, the lithium secondary battery may include a separator. In this case, the separator may be a separator that is supported on an electrolyte and then cured (e.g., UV cured) so that the electrolyte is cured in the voids. The separator is relatively thinner than the electrodes, so that the electrolyte contained in the voids can be easily cured.

[0139] Furthermore, the lithium secondary battery of the present invention does not need to contain a liquid electrolyte that is injected during the manufacture of conventional lithium secondary batteries. Specifically, the above-described electrolyte of the present invention can be uniformly hardened in the electrode, thereby fulfilling the role of a conventional liquid electrolyte.

[0140] The lithium secondary battery of the present invention can be manufactured by placing the electrode assembly described above in a cylindrical or prismatic battery case and sealing it. The battery case may be one commonly used in the art, and its shape is not limited depending on the intended use of the battery. For example, it may be cylindrical, prismatic, pouch-shaped, or coin-shaped, but is not limited thereto.

[0141] The lithium secondary battery according to one embodiment of the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery for medium- to large-sized battery modules containing multiple battery cells. Preferred examples of such medium- to large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems (ESS).

[0142] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0143] Examples and Comparative Examples Example 1 (1) Electrode slurry production An electrolyte was prepared by dissolving triacrylate (ETPTA) and 2,2'-azobis(isobutyronitrile) (AIBN) in a weight ratio of 9.9:0.1 and lithium salt LiFSI at 1.0 M in a solvent with a volume ratio of ethylene carbonate (EC) and propylene carbonate (PC) of 5:5. The triacrylate (ETPTA) and 2,2'-azobis(isobutyronitrile) (AIBN) were contained in the electrolyte at 9.9 wt% and 0.1 wt%, respectively.

[0144] The negative electrode slurry was prepared by mixing artificial graphite as a negative electrode active material and SupreC65 as a negative electrode conductive material with the electrolyte solution in a weight ratio of 98:2. The solid content of the negative electrode slurry was 75% and the viscosity at 25°C was 6,000 cP.

[0145] In addition, Li(Ni 0.8 Mn 0.1 Co 0.1 ) 02, Super C65 as a positive electrode conductive material was mixed with the electrolyte in a weight ratio of 97:3 to prepare a positive electrode slurry. At this time, the positive electrode slurry had a solid content of 75% and a viscosity of 10,000 cP at 25°C.

[0146] (2) Electrode manufacturing A 10 μm-thick copper (Cu) metal thin film was prepared as a negative electrode current collector, and the negative electrode slurry was coated on one side of the copper metal thin film. A polypropylene film was then covered on the coated negative electrode slurry. Next, the negative electrode slurry covered with the polypropylene film (thickness: 100 μm) was hot-rolled using a rolling mill with a surface temperature of 60°C. The polypropylene film was then removed from the electrode, and finally, a negative electrode with a total thickness of 85 μm was produced, in which a negative electrode active material layer and an electrolyte layer were sequentially stacked on the negative electrode current collector.

[0147] A 15 μm-thick aluminum (Al) metal thin film was prepared as a positive electrode current collector, and the positive electrode slurry was coated on one side of the aluminum metal thin film. A polypropylene film was then covered on the coated positive electrode slurry. The positive electrode slurry covered with the polypropylene film was then hot-rolled using a rolling mill with a surface temperature of 60°C. The polypropylene film was then removed from the electrode, and finally, a positive electrode with a total thickness of 65 μm was fabricated, in which a positive electrode active material layer and an electrolyte layer were sequentially stacked on the positive electrode current collector.

[0148] (3) Manufacture of lithium secondary batteries The positive and negative electrodes prepared above were arranged in contact with each other in the order of negative / positive / negative to prepare a bi-cell electrode assembly.

[0149] The electrode assembly was housed in a battery case and then sealed to manufacture a lithium secondary battery.

[0150] Example 2 An electrode slurry was produced in the same manner as in Example 1.

[0151] An electrode was produced in the same manner as in Example 1, except that an HDPE film was used instead of the polypropylene film.

[0152] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrode was used.

[0153] Example 3 An electrode slurry was produced in the same manner as in Example 1.

[0154] An electrode was manufactured in the same manner as in Example 1, except that after hot rolling with rolling rollers, the electrode was stored in a chamber with an internal temperature of 70°C for 5 hours before removing the polypropylene film from the electrode.

[0155] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrode was used.

[0156] Comparative Example 1 An electrode slurry was produced in the same manner as in Example 1.

[0157] An electrode was produced in the same manner as in Example 1, except that the electrode slurry was hot-rolled using a pressure roller without being covered with a polypropylene film.

[0158] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrode was used.

[0159] Comparative Example 2 An electrode slurry was produced in the same manner as in Example 1.

[0160] An electrode was produced in the same manner as in Example 1, except that the electrode slurry was not hot-rolled using a pressure roller, but the polypropylene film was irradiated with ultraviolet light having a wavelength of 556 nm for 1 minute.

[0161] A lithium secondary battery was manufactured in the same manner as in Example 1, except that the manufactured electrode was used.

[0162] Comparative Example 3 (1) Electrode slurry production Anode active material (artificial graphite), anode conductive material (SuperC65), and anode binder (SBR-CMC) were mixed in a weight ratio of 95:1.5:3.5 and water was used as a solvent to prepare anode slurry. The solid content of the anode slurry was 50%.

[0163] In addition, Li(Ni 0.8 Mn 0.1 Co 0.1 )02, Super C65 as a positive electrode conductive material, and PVdF as a positive electrode binder were mixed in a weight ratio of 96:1.5:2.5 and NMP was used as a solvent to prepare a positive electrode slurry. The solid content of the positive electrode slurry was 75%.

[0164] (2) Electrode manufacturing A 10 μm-thick copper (Cu) metal thin film was prepared as a negative electrode current collector, and the negative electrode slurry was coated on one side of the copper metal thin film. The negative electrode slurry was then dried and rolled to form a negative electrode active material layer on the negative electrode current collector. The electrolyte solution prepared in Example 1 was coated on the negative electrode active material layer. A polypropylene film was then covered on the coated electrolyte solution. The polypropylene film-covered electrolyte solution was then hot-rolled using a rolling mill with a surface temperature of 60°C. The hot-rolled electrode was stored in a chamber with an internal temperature of 70°C for 5 hours. The polypropylene film was then removed from the electrode, and finally, a negative electrode with a total thickness of 85 μm was fabricated, in which a negative electrode active material layer and an electrolyte layer were sequentially stacked on the negative electrode current collector.

[0165] A 15 μm-thick aluminum (Al) metal thin film was prepared as a positive electrode current collector, and the positive electrode slurry was coated on one side of the aluminum metal thin film. The positive electrode slurry was then dried and rolled to form a positive electrode active material layer on the positive electrode current collector. The electrolyte solution prepared in Example 1 was coated on the positive electrode active material layer. A polypropylene film was then covered on the coated electrolyte solution. The polypropylene film-covered electrolyte solution was then hot-rolled using a rolling mill with a surface temperature of 60°C. The hot-rolled electrode was then stored in a chamber with an internal temperature of 70°C for 5 hours. The polypropylene film was then removed from the electrode, and finally, a positive electrode with a total thickness of 65 μm was fabricated, in which a positive electrode active material layer and an electrolyte layer were sequentially stacked on the positive electrode current collector.

[0166] (3) Manufacture of lithium secondary batteries A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode and negative electrode prepared above were disposed in contact with each other to manufacture an electrode assembly.

[0167] Comparative Example 4 (1) Manufacturing of the positive electrode Li(Ni) as the positive electrode active material 0.8 Mn 0.1 Co 0.1 )02, SuperC65 as a positive electrode conductive material, and PVdF as a positive electrode binder were mixed in a weight ratio of 94:3:3, and NMP was used as a solvent to prepare a positive electrode slurry. The solid content of the positive electrode slurry was 50%. The positive electrode slurry was applied to an aluminum (Al) thin film, which serves as a positive electrode current collector, and then dried and roll-pressed to prepare a positive electrode.

[0168] (2) Manufacturing of the negative electrode Anode slurry was prepared by mixing artificial graphite as the anode active material, SuperC65 as the anode conductive material, and SBR-CMC as the anode binder in a weight ratio of 96:2:2, and using water as the solvent. The solid content of the anode slurry was 80%. The anode slurry was applied to a copper (Cu) thin film as the anode current collector, and then dried and roll-pressed to prepare the anode.

[0169] (3) Manufacturing of electrode assemblies The positive electrode, separator, and negative electrode were stacked in this order to fabricate an electrode assembly. The separator had a three-layer structure of polypropylene / polyethylene / polypropylene.

[0170] (4) Manufacture of lithium secondary batteries The electrode assembly was inserted into a pouch-type battery case, and the electrolyte prepared in Example 1 was poured into the battery case. The battery case was sealed under vacuum by applying pressure to the sealed portion of the pouch at 140°C for 2 seconds. After sealing the battery case, it was left to rest at room temperature for 3 days and then heated in a heating chamber at 70°C for 5 hours to prepare a lithium secondary battery containing a thermally polymerized gel polymer electrolyte.

[0171] [Table 1]

[0172] Experimental Example 1 - Evaluation of adhesive strength of electrode active material layer The 180° peel strength of the active material layer was measured for each of the positive electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 4.

[0173] Specifically, the positive electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were each cut to a width of 20 mm. Then, the positive electrode active material layer was peeled off from the positive electrode current collector using a UTM device, and the average 180° peel strength was measured over a displacement range of 20 to 80 mm. The measurement results are shown in Figure 2 and Table 2 below.

[0174] FIG. 2 is a graph showing the measured adhesive strength of the active material layer to the current collector for the positive electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 4.

[0175] Experimental Example 2 - Evaluation of electrode rigidity The rigidity of the positive electrodes and negative electrodes produced in Examples 1 to 3 and Comparative Examples 1 to 4 was measured.

[0176] Specifically, the positive and negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were attached to an aluminum (Al) jig with a 5 cm diameter hole, and the electrodes were then pressed with a 2 cm diameter metal rod using UTM equipment to measure their maximum stiffness. The measurement results are shown in Table 2 below.

[0177] Experimental Example 3 - Presence or absence of electrolyte leakage during the manufacturing of lithium secondary batteries In the process of manufacturing the lithium secondary batteries in Examples 1 to 3 and Comparative Examples 1 to 4, it was checked whether there was any leakage of electrolyte from the electrode assembly, and the results are shown in Table 2 below. O: Electrolyte leak X: No electrolyte leakage

[0178] Experimental Example 4: Evaluation of the capacity of a lithium secondary battery The capacity of each of the lithium secondary batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was measured. Specifically, the lithium secondary batteries were mounted on an aluminum jig using a PNE solution charge / discharge device, and then charged / discharged under the following conditions to measure the battery capacity. The measurement results are shown in Table 2 below. -Charging conditions: CC (constant current) / CV (constant voltage) mode, charging at a rate of 0.2C, cut-off at 4.2V and 0.05C -Discharge conditions: CC mode, discharge rate 0.2C, cut-off at 3.0V

[0179] Experimental Example 5: Evaluation of life characteristics of lithium secondary batteries The lithium secondary batteries produced in Examples 1 to 3 and Comparative Examples 1 to 4 were charged / discharged at a temperature of 45° C. under the following conditions, and the capacity retention rate depending on the number of cycles was measured. -Charging conditions: CC (constant current) / CV (constant voltage) mode, charging at a rate of 0.33C, cut-off at 4.2V and 0.05C -Discharge conditions: CC mode, discharge rate 0.33C, cut-off at 3.0V

[0180] At this time, the capacity retention rate of the battery was measured using an IL-2C-525S manufactured by JEIO TECH Co., Ltd. The measurement results are shown in FIG.

[0181] FIG. 3 is a graph showing the capacity retention rate as a function of the number of cycles after the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were operated at a temperature of 45° C.

[0182] [Table 2]

[0183] [Table 3]

[0184] As shown in FIGS. 2 and 3, and Tables 2 and 3, the lithium secondary batteries of Examples 1 to 3, which contain an electrode active material and a gel polymer electrolyte in the electrode active material layer and whose electrode active material layer satisfies the range of electrode rigidity, are free from electrolyte leakage, exhibit excellent capacity development, and exhibit significantly excellent life performance, compared to Comparative Examples 1 to 4, which do not.

[0185] 2 and Table 2, it can be seen that Examples 1 to 3, in which hot rolling was performed after disposing an oxygen barrier member, have significantly superior adhesive strength of the electrode active material layer compared to Comparative Example 1, in which no oxygen barrier member was used, and Comparative Example 2, in which UV curing was performed instead of thermal curing by hot rolling. Among Examples 1 to 3, it can be seen that Example 3, in which the electrolyte solution was additionally thermally cured in a high-temperature chamber, has even superior adhesive strength of the electrode active material layer compared to Examples 1 and 2.

[0186] In Comparative Example 1, in which no oxygen-blocking member was used, the electrode slurry was exposed to oxygen, and the electrolyte in the electrode was not hardened even after hot rolling. The polymer in the electrolyte was not hardened and could not function as a binder, so the adhesive strength of the electrode active material layer was significantly lower than in Examples 1 to 3.

[0187] In Comparative Example 2, in which UV curing was performed instead of hot rolling, only the electrolyte solution disposed in the upper layer of the electrode active material layer was cured, and the electrolyte solution disposed in the lower layer of the electrode active material layer was not cured. Therefore, detachment of the active material layer occurred at the boundary between the upper and lower layers of the electrode active material layer, and the adhesive strength of the electrode active material layer was significantly lower than in Examples 1 to 3.

[0188] On the other hand, as shown in Table 2, Examples 1 to 3, in which hot rolling was performed after arranging an oxygen-shielding member, were found to have significantly superior electrode rigidity compared to Comparative Example 1, in which no oxygen-shielding member was used, and Comparative Example 2, in which UV curing was performed instead of thermal curing by hot rolling. Among Examples 1 to 3, Example 3, in which the electrolyte solution was additionally thermally cured in a high-temperature chamber, was found to have superior electrode rigidity compared to Examples 1 and 2.

[0189] In Comparative Example 1, in which no oxygen-blocking member was used, the electrode slurry was exposed to oxygen, and the electrolyte in the electrode was not hardened even after hot rolling. As a result, the electrode rigidity was significantly lower than in Examples 1 to 3.

[0190] In Comparative Example 2, in which UV curing was performed instead of hot rolling, only the electrolyte placed on the surface of the electrode was cured, but not the electrolyte placed inside the electrode, resulting in significantly lower electrode rigidity than in Examples 1 to 3.

[0191] On the other hand, as shown in Table 2, in Comparative Example 1, in which no oxygen barrier member was used, and Comparative Example 2, in which UV curing was performed instead of thermal curing by hot rolling, the electrolyte in the electrode was not sufficiently cured, and it was confirmed that the electrolyte leaked out of the electrode assembly during cell assembly.

[0192] On the other hand, as shown in FIG. 3 and Tables 2 to 3, in Comparative Example 3 in which a general electrode was impregnated with an electrolyte solution and then thermally cured, the electrolyte solution did not penetrate deep into the electrode, and therefore no thermally cured electrolyte was present inside the electrode. As a result, it was confirmed that the battery capacity and the battery capacity retention rate were significantly lower than those of Examples 1 to 3.

[0193] In addition, Comparative Example 4 exhibits low electrode rigidity due to the presence of unreacted monomers in the gel polymer electrolyte or insufficient impregnation of the electrode with the gel polymer electrolyte, resulting in low capacity and reduced life performance. [Explanation of symbols]

[0194] 10 electrodes 110 Electrode current collector 120 Electrode active material layer 130 Coating layer (or electrolyte layer)

Claims

1. an electrode current collector; an electrode active material layer disposed on at least one surface of the electrode current collector, the electrode active material layer contains an electrode active material and a gel polymer electrolyte, An electrode having an electrode rigidity of 2 kPa or more and 4 kPa or less.

2. The electrode according to claim 1 , wherein the gel polymer electrolyte is impregnated inside the electrode active material layer.

3. the electrode is a positive electrode, the electrode active material is a positive electrode active material, The electrode of claim 1 , wherein the positive electrode active material comprises a lithium nickel cobalt-based composite oxide represented by the following Chemical Formula 1: [Chemical formula 1] Li １＋ｘ (N ａ Co ｂ Mn ｃ M ｄ )O ２ (In the above chemical formula 1, M is one or more selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; 1 + x, a, b, c, and d are each independently mole ratios of elements; -0.2≦x≦0.2, 0.60≦a<1, 0<b≦0.30, 0<c≦0.30, 0≦d≦0.10, a+b+c+d=1.)

4. the electrode is a negative electrode, the electrode active material is a negative electrode active material, The electrode of claim 1 , wherein the negative electrode active material is a carbon-based material.

5. the gel polymer electrolyte is a cured product of an electrolytic solution containing a crosslinkable material, a lithium salt, and an organic solvent; The electrode according to claim 1 , wherein the crosslinkable substance comprises at least one selected from a crosslinkable monomer and a crosslinkable oligomer.

6. The electrode active material layer further includes a coating layer disposed on a surface opposite to the surface facing the electrode current collector, The electrode of claim 1 , wherein the coating layer comprises a gel polymer electrolyte.

7. Coating an electrode current collector with an electrode slurry containing an electrolyte; placing an oxygen barrier member on the coated electrode slurry; and hot-rolling the electrode slurry covered with the oxygen barrier member, the electrolytic solution is thermally cured by the hot rolling.

8. The method for manufacturing an electrode according to claim 7 , wherein the hot rolling step includes a step of rolling the electrode slurry with a rolling roller having a surface temperature of 30° C. or more and 80° C. or less.

9. The method for producing an electrode according to claim 7, wherein the thickness of the electrode after the hot rolling is 50 μm or more and 1,000 μm or less.

10. The method for manufacturing an electrode according to claim 7 , wherein the oxygen barrier member comprises a flexible material.

11. The method for manufacturing an electrode according to claim 10, wherein the oxygen barrier member comprises at least one material selected from the group consisting of polypropylene (PP) and high density polyethylene (HDPE).

12. further comprising the step of heating the electrode after the hot rolling; The method for manufacturing an electrode according to claim 7 , wherein the electrolytic solution in the electrode is further thermally cured by the heating step.

13. The method for manufacturing an electrode according to claim 12 , wherein the heating step includes a step of storing the electrode at a temperature of 40° C. or higher and 80° C. or lower for 10 minutes or longer and 24 hours or shorter.

14. The method for manufacturing an electrode according to claim 7 , wherein the electrode slurry is manufactured by mixing the electrolytic solution with an active material and a conductive material.

15. The method for producing an electrode according to claim 7 , wherein the electrode slurry does not contain a binder or N-methyl-2-pyrrolidone (NMP).

16. The method for producing an electrode according to any one of claims 7 to 15, wherein the electrolyte solution contains at least one of a monomer and an oligomer in an amount of 4% by weight or more and 40% by weight or less.

17. 17. The method for producing an electrode according to claim 16, wherein the monomer comprises one or more selected from the group consisting of ethylene glycol diacrylate, triethylene glycol diacrylate, ethoxylated trimethylolpropane triacrylate (ETPTA), bisphenol A ethoxylated dimethacrylate, acrylic acid, carboxyethyl acrylate, carboxyethyl acrylate, methyl cyanoacrylate, ethyl cyanoacrylate, ethyl cyanoethoxyacrylate, cyanoacrylic acid, hydroxyethyl methacrylate, and hydroxypropyl acrylate.

18. 17. The method for producing an electrode according to claim 16, wherein the oligomer comprises at least one selected from the group consisting of polyether-based oligomers, polycarbonate-based oligomers, acrylate-based oligomers, polysiloxane-based oligomers, phosphazene-based oligomers, polyethylene-based oligomers, urethane-based oligomers, epoxy-based oligomers, fluorine-based oligomers, polyethylene oxide, polyester sulfide, polyvinyl alcohol, and polyvinylidene fluoride.

19. A lithium secondary battery comprising the electrode according to any one of claims 1 to 6.

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