Electrode for lithium secondary battery including insulating layer and method for producing same

Abstract

The lithium secondary battery electrode of the present invention includes an insulating layer, the insulating layer including a first insulating layer including a first binder, and a second insulating layer formed on the first insulating layer and including inorganic particles and a second binder, the first binder being PVDF (Polyvinylidene fluoride) and the second binder being SBR (styrene butadiene rubber). This allows the insulating layer of the present invention to have excellent wet adhesion and electrical safety.

Description

[Technical field]

[0001] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0162675, filed November 23, 2021.

[0002] The present invention relates to an electrode for a lithium secondary battery including an insulating layer having a multi-layer structure, which has excellent wet adhesion, coating properties and electrical safety, and a method for manufacturing the same. [Background technology]

[0003] 2. Description of the Related Art With the increasing technological development and demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Accordingly, much research is being conducted on batteries that can meet various demands.

[0004] Typically, in terms of battery shape, there is a high demand for prismatic and pouch-shaped batteries that are thin and can be applied to products such as mobile phones, and in terms of materials, there is a high demand for lithium secondary batteries such as lithium cobalt polymer batteries that have high energy density, discharge voltage, and output stability.

[0005] One of the main research topics for secondary batteries is to improve their safety. The main cause of safety-related accidents in batteries is the arrival of abnormal high temperature conditions due to short circuits between the positive and negative electrodes. In other words, under normal circumstances, a separator between the positive and negative electrodes maintains electrical insulation, but in abnormal circumstances such as when the battery is overcharged or overdischarged, when an internal short circuit occurs due to dendritic growth of the electrode material or a foreign object, when a sharp object such as a nail or screw penetrates the battery, or when an external force causes excessive deformation of the battery, the existing separator reaches its limits.

[0006] Generally, a microporous membrane made of polyolefin resin is used as a separator, but its heat resistance is insufficient, being only about 120 to 160°C. Therefore, when an internal short circuit occurs, the separator shrinks due to the short circuit reaction heat, expanding the short circuit area, leading to a thermal runway state in which a large amount of reaction heat is generated at a higher temperature. This phenomenon mainly occurs at the electrode active material-coated end of the electrode current collector coated with the electrode active material when the electrodes are stacked, and therefore various methods have been attempted to reduce the possibility of short circuiting of electrodes under external impact or high temperature.

[0007] Specifically, in order to solve the internal short circuit of a battery, a method has been proposed in which an insulating layer is formed by attaching an insulating tape to the uncoated portion of the electrode and a part of the composite layer or by applying an insulating liquid for forming an insulating layer. For example, a binder for insulating purposes is applied to the uncoated portion of the positive electrode and a part of the positive electrode composite layer, or an insulating liquid for forming an insulating layer in which a mixture of the binder and inorganic particles is dispersed in a solvent is applied.

[0008] Such insulating liquid for forming an insulating layer contains inorganic particles and a color former in a polyvinylidene fluoride (PVDF) binder, and conventionally, an insulating layer has been formed by applying such insulating liquid for forming an insulating layer in a single layer. Although an insulating layer containing a PVDF-based binder has advantages such as excellent electrical safety and coating processability, when wetted with an electrolyte, the adhesive strength decreases, and the insulating layer may detach from the current collector or the electrode mixture layer, which is an impediment to the safety of the battery.

[0009] Therefore, there is a need for technological development for electrodes including an insulating layer that has excellent wet adhesion while also being excellent in electrical safety. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is intended to solve the above-mentioned problems of the conventional art, and provides an electrode for a lithium secondary battery including an insulating layer that has excellent adhesive strength between a current collector and an electrode mixture layer and also has excellent electrical safety. [Means for solving the problem]

[0011] The electrode for a lithium secondary battery according to the present invention includes a current collector, an electrode mixture layer formed on one or both sides of the current collector, and an insulating layer, the insulating layer including a first insulating layer including a first binder, and a second insulating layer formed on the first insulating layer and including inorganic particles and a second binder, the first binder being PVDF (Polyvinylidene fluoride), and the second binder being SBR (styrene butadiene rubber).

[0012] In one embodiment of the present invention, the current collector includes an uncoated portion where the electrode mixture layer is not formed, and the first insulating layer may cover from a portion of the uncoated portion to a portion of the electrode mixture layer.

[0013] In one embodiment of the present invention, the second insulating layer may cover from a portion of the uncoated portion to a portion of the electrode mixture layer.

[0014] In one embodiment of the present invention, the surface of the first insulating layer may be completely covered by the second insulating layer.

[0015] In one embodiment of the present invention, the inorganic particles may be one or a mixture of two or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, TiO2, MgO, CaO, Cr2O3, MnO2, Fe2O3, CoO4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide (SiC), and boron nitride (BN).

[0016] In one embodiment of the present invention, the first insulating layer further includes an additional binder and inorganic particles in addition to the first binder, and the additional binder may be one or a mixture of two or more selected from the group consisting of polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

[0017] In one embodiment of the present invention, the second insulating layer further includes an additional binder in addition to the second binder, and the additional binder may be one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride copolymer, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

[0018] In one embodiment of the present invention, the first insulating layer may contain 20% to 99% by weight of a binder.

[0019] In one embodiment of the present invention, the second insulating layer may contain 20% to 99% by weight of a binder.

[0020] In one embodiment of the present invention, the first insulating layer and the second insulating layer may each have a thickness of 1 μm to 15 μm.

[0021] A method for manufacturing an electrode for a lithium secondary battery according to one embodiment of the present invention includes a step of mixing a binder component containing a solvent and a first binder to prepare an insulating liquid for forming a first insulating layer, a step of mixing a binder component containing inorganic particles, a solvent and a second binder to prepare an insulating liquid for forming a second insulating layer, a step of applying an electrode mixture slurry containing an electrode active material onto a current collector, and an insulating liquid application step of applying the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer.

[0022] In one embodiment of the present invention, the insulating liquid applying step may include applying the insulating liquid for forming a second insulating layer on a coating layer of the insulating liquid for forming a first insulating layer.

[0023] In an embodiment of the present invention, the insulating liquid applying step may be performed such that a surface of the insulating liquid for forming the first insulating layer is completely covered with the insulating liquid for forming the second insulating layer.

[0024] In one embodiment of the present invention, the viscosity of the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer may be 1,000 cps to 10,000 cps at 25°C, respectively.

[0025] In one embodiment of the present invention, the viscosity of the insulating liquid for forming the second insulating layer may be lower than the viscosity of the insulating liquid for forming the first insulating layer.

[0026] In one embodiment of the present invention, the solvent of the insulating liquid for forming the first insulating layer and the solvent of the insulating liquid for forming the second insulating layer may be the same.

[0027] The lithium secondary battery according to the present invention includes the above-mentioned electrode as a positive electrode or a negative electrode. Effect of the Invention

[0028] The electrode for a lithium secondary battery of the present invention includes an insulating layer that includes a first insulating layer having excellent electrical safety and a second insulating layer having excellent wet adhesion, and the second insulating layer located in the upper layer blocks or inhibits the penetration of an electrolyte into the first insulating layer located in the lower layer, thereby including an insulating layer that has excellent electrical safety and excellent wet adhesion. [Brief description of the drawings]

[0029] [Figure 1] 1 is a cross-sectional view of an electrode for a lithium secondary battery according to one embodiment of the present invention. [Diagram 2] FIG. 4 is a cross-sectional view of an electrode for a lithium secondary battery according to another embodiment of the present invention. [Diagram 3]1 is a diagram showing a method for applying an insulating liquid for forming an insulating layer according to an embodiment of the present invention. [Figure 4] 4 is a view showing a method of applying an insulating liquid for forming an insulating layer according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings. Before that, the terms and words used in the specification and claims are not to be interpreted as being limited to their ordinary or dictionary meanings, but are to be interpreted as meanings and concepts that are consistent with the technical ideas of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to best describe his / her invention.

[0031] Therefore, it should be understood that the embodiment described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can replace them at the time of this application.

[0032] As used herein, terms such as "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, steps, components, or combinations thereof, and are to be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

[0033] The present invention will now be described in more detail.

[0034] <Electrodes for lithium secondary batteries> FIG. 1 is a cross-sectional view of an electrode for a lithium secondary battery according to one embodiment of the present invention. Referring to FIG. 1, the electrode for a lithium secondary battery of the present invention includes a current collector 10, an electrode mixture layer 20 formed on one or both sides of the current collector, and an insulating layer 30. The insulating layer includes a first insulating layer 31 containing a first binder, and a second insulating layer 32 formed on the first insulating layer and containing inorganic particles and a second binder. The first binder is PVDF (Polyvinylidene fluoride), and the second binder is SBR (styrene butadiene rubber).

[0035] The insulating layer of the present invention is a multi-layer structure including a first insulating layer and a second insulating layer formed on the first insulating layer, and the first insulating layer includes PVDF, which has excellent electrical safety and coating processability, as a first binder. In order to improve the problem of the first insulating layer that the adhesive strength decreases when wet with an electrolyte, a second insulating layer that blocks or inhibits the wetting of the electrolyte of the first insulating layer is applied onto the first insulating layer, and the second insulating layer includes a second binder that has excellent wet adhesive strength. Therefore, the insulating layer of the present invention has excellent electrical safety and wet adhesive strength.

[0036] In the electrode of the present invention, the current collector includes an uncoated portion on which the electrode mixture layer is not formed, and the insulating layer is formed on the uncoated portion on the current collector on which the electrode mixture layer is not applied, or is formed so as to partially overlap the electrode mixture layer.

[0037] The first insulating layer is applied so as to cover from a part of the uncoated portion to a part of the electrode mixture layer. In this case, the length of the region where the first insulating layer overlaps with the electrode mixture layer may be 0.05 mm to 5 mm, preferably 0.1 mm to 3.0 mm.

[0038] In order to prevent a decrease in capacity due to overlapping of the electrode mixture layer and the first insulating layer, the thickness of the first insulating layer in the region overlapping with the electrode mixture layer may decrease toward the electrode mixture layer.

[0039] The second insulating layer is applied so as to cover from a part of the uncoated portion to a part of the electrode mixture layer.

[0040] Fig. 2 is a cross-sectional view of an electrode according to another embodiment of the present invention. Referring to Fig. 2, the surface of the first insulating layer 31 may be completely covered with the second insulating layer 32. That is, the second insulating layer overlaps a part of the current collector 10, the entire first insulating layer 31, and a part of the electrode mixture layer 20. In this case, the length of the overlap of the second insulating layer with the current collector is 0.05 mm to 5 mm, preferably 0.1 mm to 3.0 mm.

[0041] When the first insulating layer and the second insulating layer are formed in such a structure, the first insulating layer is not exposed to the outside, and therefore the second insulating layer can more fully perform its function as a protective layer that blocks or inhibits the electrolyte from penetrating into the first insulating layer.

[0042] Since the second insulating layer functions to protect the first insulating layer from being wetted by the electrolyte, it is preferable that the second insulating layer has excellent wet adhesion.

[0043] Such a second insulating layer includes inorganic particles and a second binder, and the second binder is one or more selected from the group consisting of styrene butadiene rubber, acrylate styrene butadiene rubber, acrylonitrile butadiene rubber, and acrylonitrile butadiene-styrene rubber, of which styrene butadiene rubber (SBR, hereinafter referred to as "SBR") is most preferred.

[0044] The above SBR contains repeating units derived from styrene monomers and repeating units derived from butadiene monomers in a weight ratio of 70:30 to 30:70, and by containing repeating units derived from styrene monomers having hydrophobic groups within the above range, the wet adhesion strength of the second insulating layer can be improved.

[0045] In addition, the total weight of the repeating units derived from the styrene monomer and the repeating units derived from the butadiene monomer may be 30 to 100% or 30 to 70% by weight based on the total weight of the styrene-butadiene rubber, and when such a range is satisfied, the wet adhesion of the second insulating layer is suitably controlled.

[0046] Examples of the styrene monomer include styrene, α-methylstyrene, p-methylstyrene, 3-methylstyrene, 4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene, 1-vinyl-5-hexylnaphthalene, derivatives thereof, and mixtures thereof. Examples of the butadiene monomer include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, derivatives thereof, and mixtures thereof.

[0047] If necessary, the SBR may further contain a repeating unit derived from a monomer having a crosslinking group, preferably in an amount of 12 parts by weight or less based on the total weight of the SBR in order to reduce the electrolyte absorption rate.

[0048] The first binder contained in the first insulating layer is polyvinylidene fluoride (PVDF, hereinafter referred to as "PVDF") from the viewpoints of adhesion to the electrode mixture layer, chemical resistance, and electrochemical stability. The PVDF includes a PVDF-based polymer containing vinylidene fluoride (VDF) as a monomer. Specific examples of the PVDF-based polymer include a PVDF single polymer, PVDF copolymers such as PVDF-HFP (Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-CTFE (Poly(vinylidene fluoride-co-chlorotrifluoroethylene), PVDF-TFE (Poly(vinylidene tetrafluoroethylene), polyvinylidene tetrafluoroethylene), and PVDF-TrFE (Poly(vinylidene trifluoroethylene), polyvinylidene trifluoroethylene).

[0049] The PVDF may have a weight average molecular weight of 400,000 to 1,500,000, and preferably 600,000 to 1,200,000, from the standpoint of improving the adhesive strength with the electrode mixture layer and ensuring the desired viscosity.

[0050] The PVDF binder contained in the first insulating layer maintains its molecular structure well without side reactions even when it is charged and discharged for a long period of time at a voltage level of 4V to 5V due to its electrochemical stability, but the wet adhesion strength is reduced by the electrolyte, so there is a possibility that it may be detached from the current collector and the electrode mixture layer. The SBR, which is the binder contained in the second insulating layer, has excellent wet adhesion strength, but when it is charged and discharged for a long period of time at a voltage level of 4V to 5V, it may be decomposed due to an oxidation reaction of butadiene in the SBR. However, the PVDF contained in the first insulating layer can mitigate such an oxidation reaction, and the first insulating layer remains even if the oxidation reaction proceeds, so that the insulating properties of the insulating layer can be maintained.

[0051] The first insulating layer may further include an additional binder in addition to the first binder, and specific examples of the additional binder include one or a mixture of two or more selected from the group consisting of polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

[0052] The second insulating layer may further include an additional binder in addition to the second binder, and specific examples of the additional binder include one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride copolymer, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

[0053] By including such additional binders in the first and second insulating layers, respectively, the shortcomings of PVDF and SBR can be compensated for.

[0054] The first insulating layer and the second insulating layer may further include inorganic particles, which can improve the safety of the battery and can also improve the strength of the insulating layer. The content of the inorganic particles may be suitably adjusted in consideration of the viscosity, heat resistance, insulation, filling effect, dispersibility or stability of the insulating liquid for forming the insulating layer. In general, the larger the diameter of the inorganic particles, the higher the viscosity of the insulating liquid containing them, and the higher the possibility of settling in the insulating liquid. In addition, the smaller the diameter of the inorganic particles, the higher the heat resistance tends to be. Therefore, in consideration of the above points, inorganic particles of a suitable type and size may be selected, and two or more types of inorganic particles may be used together if necessary.

[0055] In a specific example, the inorganic particles may be one or a mixture of two or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, TiO2, MgO, CaO, Cr2O3, MnO2, Fe2O3, CoO4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide (SiC), and boron nitride (BN).

[0056] The first insulating layer and the second insulating layer may each contain the inorganic particles in an amount of up to 60% by weight, preferably 5% to 55% by weight, and more preferably 5% to 50% by weight.

[0057] In a specific example, the first insulating layer may contain 20% to 99% by weight of a binder, and the second insulating layer may contain 20% to 99% by weight of a binder.

[0058] In a specific example, the thickness of each of the first insulating layer and the second insulating layer is 1 μm to 15 μm, preferably 2 μm to 13 μm, and more preferably 3 μm to 12 μm.

[0059] In the second insulating layer, the weight ratio of the inorganic particles to SBR may be in the range of 1:99 to 95:5, or may be in the range of 10:90 to 70:30, or 20:80 to 50:50. When the ratio is in the above range, it is advantageous in terms of adhesion between inorganic particles, adhesion between the insulating layer and the current collector, and the desired insulating effect.

[0060] The electrode may be a positive electrode or a negative electrode, whereby the electrode mixture layer may be a positive electrode mixture layer containing a positive electrode active material, or a negative electrode mixture layer containing a negative electrode active material.

[0061] The positive electrode is manufactured by applying a mixture of a positive electrode active material, a conductive material, and a binder onto a positive electrode current collector and then drying the mixture. If necessary, a filler may be further added to the mixture.

[0062] The positive electrode current collector is generally made to a thickness of 3 to 500 μm. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery, and for example, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The current collector may have fine irregularities on its surface to increase the adhesive force of the positive electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc.

[0063] The positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or a compound substituted with one or more transition metals; the chemical formula is Li 1+x Mn 2-x Lithium manganese oxides such as LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-x M x Lithium nickel oxide with Ni site represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x=0.01 to 0.3); 2-x M x Examples of such compounds include, but are not limited to, lithium manganese composite oxides represented by Li2Mn3MO8 (wherein M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 to 0.1) or Li2Mn3MO8 (wherein M is Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is replaced with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3.

[0064] The negative electrode is produced by applying a negative electrode material onto a negative electrode current collector and drying the applied material, and may further contain the components described above, if necessary.

[0065] The above-mentioned negative electrode current collector is generally made with a thickness of 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has high conductivity without inducing chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, those with surface treatment of 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 can 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 fabrics, etc.

[0066] In a specific example, the above-mentioned negative electrode active material includes carbon such as graphitizable carbon and graphite-based carbon; Li x Fe2O3(0 ≦ x ≦ 1), Li x WO2(0 ≦ x ≦ 1), Sn x Me 1-x Me’ y O z (Me: Mn, Fe, Pb, Ge; Me’: Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, halogen; 0 < x ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8), etc. metal composite oxides; lithium metal; lithium alloy; silicon-based alloy; tin-based alloy; metal oxides such as SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4, and Bi2O5; conductive polymers such as polyacetylene; Li-Co-Ni-based materials, etc. can be used.

[0067] The conductive material is usually added in an amount of 1 to 50% by weight based on the weight of the entire mixture including the positive electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without inducing a chemical change in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; conductive fibers such as carbon fiber and metal fiber; metal powders such as carbon fluoride, aluminum, 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.

[0068] The binder is a component that aids in binding between the active material and the conductive material and to the current collector, and is generally added in an amount of 1 to 50% by weight based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butylene rubber, fluorine rubber, and various copolymers.

[0069] <Method of manufacturing electrodes for lithium secondary batteries> The method for manufacturing an electrode for a lithium secondary battery according to the present invention includes a step of mixing a binder component containing a solvent and a first binder to prepare an insulating liquid for forming a first insulating layer, a step of mixing a binder component containing inorganic particles, a solvent and a second binder to prepare an insulating liquid for forming a second insulating layer, a step of applying an electrode mixture slurry containing an electrode active material onto a current collector, and an insulating liquid application step of applying the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer.

[0070] The step of preparing an insulating liquid for forming a first insulating layer is a step of preparing an insulating liquid for forming an insulating layer by mixing PVDF as a first binder into a solvent, and the step of preparing an insulating liquid for forming a second insulating layer is a step of preparing an insulating liquid for forming an insulating layer by mixing SBR and inorganic particles as a second binder into a solvent.

[0071] The solvents used in the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer may include water; alcohols such as methanol, ethanol, propanol, and butanol; ketones such as acetone and ethyl ketone; ethers such as methyl ethyl ether, diethyl ether, and diisoamyl ether; lactones such as γ-butyrolactone; N-methyl-2-pyrrolidone (NMP); lactams such as β-lactam; cycloaliphatic compounds such as cyclopentane and cyclohexane; aromatic hydrocarbons such as benzene and toluene; esters such as methyl lactate and ethyl lactate. Among these, N-methyl-2-pyrrolidone (NMP), which has similarity to existing positive electrode mixture slurries, may be preferably used. The content of the solvent is not particularly limited, but is determined in consideration of the dispersibility of inorganic particles, the ease of coating, and the drying time.

[0072] The step of applying the electrode mixture slurry includes a step of applying the mixture slurry composition on an electrode current collector to form a wet electrode mixture layer. The electrode current collector may be of the same type, material, thickness, etc. as the electrode current collector described above.

[0073] The mixture slurry composition can be applied onto the electrode current collector to form the wet electrode mixture layer.

[0074] For example, the above-mentioned wet electrode mixture layer can form an electrode mixture layer after simultaneous drying with a wet insulating layer described below.

[0075] The above-mentioned electrode mixture slurry composition may be a positive electrode mixture slurry composition or a negative electrode mixture slurry composition, preferably a positive electrode mixture slurry composition.

[0076] The positive electrode mixture slurry composition may contain a positive electrode mixture binder and / or a conductive material, and the negative electrode mixture slurry composition may contain a negative electrode mixture binder and / or a conductive material. The positive electrode mixture, negative electrode mixture binder and / or conductive material may be the above-mentioned positive electrode mixture, negative electrode mixture binder and / or conductive material.

[0077] The mixture slurry composition can be applied onto the electrode current collector to form a wet electrode mixture layer. In this specification, "undried" includes not only the case where the mixture slurry composition is not dried after application, but also the case where no drying step is performed and the mixture is not substantially dried.

[0078] In one embodiment of the present invention, the insulating layer may be formed by applying and drying an electrode mixture slurry containing an electrode active material to an electrode collector to form an electrode mixture layer, and then applying and drying the insulating layer-forming insulating liquid to an uncoated portion of the electrode collector.

[0079] The coating method for forming the insulating layer may include, but is not limited to, dipping, spray coating, spin coating, roll coating, die coating, gravure printing, bar coating, etc., and preferably, die coating and gravure printing methods may be used.

[0080] The insulating liquid applying step includes applying the insulating liquid to the wet electrode active material layer so as to partially overlap the wet insulating layer, thereby forming a wet insulating layer.

[0081] The insulating liquid applying step is performed by applying the insulating liquid for forming the second insulating layer onto the applied portion of the insulating liquid for forming the first insulating layer.

[0082] Fig. 3 illustrates a method for forming an insulating layer according to an embodiment of the present invention. Referring to Fig. 3, in one specific example, two single die coaters 210 and 220 are used, one single die coater 210 discharges the insulating liquid 31 for forming the first insulating layer, and the other single die coater 220 discharges the insulating liquid 32 for forming the second insulating layer, and the insulating liquid for forming the second insulating layer is discharged on top of the insulating liquid for forming the first insulating layer, thereby forming the insulating layer of the present invention.

[0083] Fig. 4 illustrates a method for forming an insulating layer according to another embodiment of the present invention. Referring to Fig. 4, a dual die coater 300 is used to eject a first insulating layer forming insulating liquid 31 and a second insulating layer forming insulating liquid 32 from two slits, respectively, to form a first insulating layer and a second insulating layer almost simultaneously, thereby simplifying the insulating layer coating process and improving productivity.

[0084] At this time, it is preferable to apply the insulating liquid for forming the first insulating layer so that the surface of the insulating liquid for forming the second insulating layer is completely covered with the insulating liquid for forming the second insulating layer, so that the second insulating layer does not wet the first insulating layer with the electrolytic solution.

[0085] The first insulating layer forming insulating liquid and the second insulating layer forming insulating liquid each have a viscosity of 1,000 cps to 10,000 cps at 25°C.

[0086] In a specific example, the viscosity of the insulating liquid for forming the second insulating layer may be adjusted to be in a range smaller than the viscosity of the insulating liquid for forming the first insulating layer so that the insulating liquid for forming the second insulating layer can completely cover the application site of the insulating liquid for forming the first insulating layer.

[0087] The coating thickness of each of the first insulating layer-forming insulating liquid and the second insulating layer-forming insulating liquid is 1 μm to 15 μm, preferably 2 μm to 14 μm, and more preferably 3 μm to 12 μm. If the coating thickness of the insulating layer-forming insulating liquid is too thin, it is difficult to expect an insulating effect, whereas if it is too thick, the volume of the electrode tab becomes unnecessarily large, which is not preferable.

[0088] The binder and inorganic particles contained in the first insulating layer and the second insulating layer have been described in detail above, so further description will be omitted.

[0089] <Lithium secondary battery> The lithium secondary battery according to the present invention includes an electrode including the above-mentioned first insulating layer and second insulating layer as a positive electrode or a negative electrode.

[0090] Specifically, the lithium secondary battery includes a positive electrode, a negative electrode facing the positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode and / or the negative electrode may be the above-mentioned lithium secondary battery electrodes. The lithium secondary battery may further include a battery container that houses an electrode assembly of the positive electrode, the negative electrode, and the separator, and a sealing member that seals the battery container.

[0091] Meanwhile, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode to provide a path for lithium ions to move. Any separator that is generally used as a separator in a lithium secondary battery can be used without any particular limitation. In particular, a separator that has low resistance to ion movement of the electrolyte and has excellent electrolyte humidification ability is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof can be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting point glass fiber, polyethylene terephthalate fiber, etc. can be used. In addition, a coated separator containing a ceramic component or a polymeric material can be used to ensure heat resistance or mechanical strength, and can be selectively used in a single layer or multilayer structure.

[0092] In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0093] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0094] The present invention will be described in more detail with reference to the following examples. However, the configurations described in the examples described in this specification are merely examples of the present invention and do not represent all of the technical ideas of the present invention, so it should be understood that there may be various equivalents and modifications that can replace them at the time of filing this application.

[0095] The organic solvent may be used without any particular limitation as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvent may be an ester solvent such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, or the like; dibutyl ether; Ether-based solvents such as ether or tetrahydrofuran; ketone-based solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; carbonate-based solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylenecarbonate (EC), and propylenecarbonate (PC); alcohol-based solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a straight-chain, 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; or sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of enhancing the charge / discharge performance of a battery and a low-viscosity linear carbonate-based compound (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.) is more preferred. In this case, the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9 to obtain excellent performance of the electrolyte.

[0096] The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt may be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably within the range of 0.1 to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, so that it can exhibit excellent electrolyte performance and lithium ions can move effectively.

[0097] In addition to the electrolyte components, the electrolyte may further contain one or more additives such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, 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, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing the decrease in the capacity of the battery, improving the discharge capacity of the battery, etc. In this case, the additives may be contained in an amount of 0.1 to 5 wt % based on the total weight of the electrolyte.

[0098] The lithium secondary batteries according to the embodiments are useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0099] According to another embodiment of the present invention, there is provided a battery module including the lithium secondary battery as a unit cell, and a battery pack including the same.

[0100] The battery module or battery pack may be used as a power source for one or more medium- to large-sized devices including power tools; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0101] The shape of the lithium secondary battery of the present invention is not particularly limited, but may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0102] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for a small device, but also preferably as a unit battery for a medium- to large-sized battery module including a large number of battery cells.

[0103] The present invention will now be described in more detail with reference to examples and experimental examples.

[0104] However, the following examples and experimental examples are merely illustrative of the present invention, and the contents of the present invention are not limited to the following examples and experimental examples.

[0105] (Example: Production of insulating liquid for forming insulating layer) <Production of insulating liquid for forming first insulating layer> PVDF (product name: KF9700, manufacturer: Kureha, weight average molecular weight: 880,000) as the first binder and AlOOH as the inorganic particles were added to N-methyl-2-pyrrolidone (NMP) solvent and stirred. At this time, the weight ratio of the first binder to the inorganic particles was 60:40.

[0106] <Production of insulating liquid for forming second insulating layer> A commercially available SBR as a second binder and AlOOH as inorganic particles were added to the water solvent and stirred, with the weight ratio of the second binder to the inorganic particles being 60:40.

[0107] (Comparative Example: Production of Insulating Liquid for Forming Insulating Layer) An insulating liquid for forming an insulating layer was prepared by the same method as that for the first insulating layer forming insulating liquid of the above-mentioned Example.

[0108] (Experimental Example 1: Measurement of Wet Adhesion Strength) In order to evaluate the wet adhesion of the insulating layer according to the present invention, the following experiment was carried out.

[0109] <Preparation of specimen with insulating layer> The insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer were coated on an aluminum metal foil having a thickness of 15 μm in a sequential manner so as to be laminated, and then dried to prepare a test specimen. The thickness of each of the first insulating layer and the second insulating layer of the test specimen was 5 μm. The metal test specimen of the embodiment having the insulating layer formed thereon was punched out to a size of 2 cm x 2 cm using a punch for measuring adhesive strength.

[0110] For the comparative example, a test piece was prepared in the same manner as above.

[0111] <Ultrasonic application> 200 g of electrolyte EC / EMC=3 / 7 (vol.%) was placed in a 250 ml beaker, and each specimen of the examples and comparative examples having an insulating layer was impregnated with the electrolyte. The specimen was fixed with a jig to control the movement of the specimen.

[0112] Then, ultrasonic waves were applied to the electrolyte in which the specimens were immersed using an ultrasonic disperser (BANDELIN, 4200). The ultrasonic application conditions were as follows:

[0113] - Frequency: 20kHz - Tip diameter: 13mm (TS-113) - Amplitude: 100% (Peak-to-peak 132μm when using a 13mm tip)

[0114] Then, ultrasonic waves were applied until the temperature of the electrolyte reached 109° C., and the specimens were visually inspected for detachment of the insulating layer. The results are shown in Table 1.

[0115] [Table 1]

[0116] As shown in Table 1, the insulating layer did not detach from the specimen of the Example, but the insulating layer detached from the specimen of Comparative Example 1. Therefore, it can be confirmed that the electrode according to the present invention has excellent wet adhesion due to the presence of the second insulating layer.

Claims

1. A current collector; an electrode mixture layer formed on one or both surfaces of the current collector; an insulating layer; the insulating layer includes a first insulating layer including a first binder, and a second insulating layer formed from on the first insulating layer to a portion of the electrode mixture layer, the second insulating layer including inorganic particles and a second binder; the first binder is polyvinylidene fluoride (PVDF); the second binder is styrene butadiene rubber (SBR); the current collector includes a plain portion on which the electrode mixture layer is not formed, The electrode for a lithium secondary battery, wherein the first insulating layer covers from a part of the uncoated portion to a part of the electrode mixture layer.

2. The electrode for a lithium secondary battery according to claim 1 , wherein the second insulating layer covers from a portion of the uncoated portion to a portion of the electrode mixture layer.

3. 2. The electrode for a lithium secondary battery according to claim 1, wherein a surface of the first insulating layer is completely covered with the second insulating layer.

4. The inorganic particles include AlOOH, Al ２ O ３ , γ-AlOOH, Al(OH) ３ , Mg(OH) ２ , Ti(OH) ４ , TiO ２ , MgO, CaO, Cr ２ O ３ , MnO ２ , Fe ２ O ３ , CoO ４ , NiO, ZrO ２ , BaTiO ３ , SnO ２ , CeO ２ , Y ２ O ３ , SiO ２ 2. The electrode for a lithium secondary battery according to claim 1, which is one or a mixture of two or more selected from the group consisting of silicon carbide and boron nitride.

5. The first insulating layer further comprises an additional binder and inorganic particles; 2. The electrode for a lithium secondary battery according to claim 1, wherein the additional binder is one or a mixture of two or more selected from the group consisting of polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

6. the second insulating layer further comprises an additional binder; 2. The electrode for a lithium secondary battery according to claim 1, wherein the additional binder is one or a mixture of two or more selected from the group consisting of polyvinylidene fluoride copolymer, polyvinyl alcohol, polyethylene oxide, cellulose acetate, polyacrylonitrile, polyacrylate rubber, polymethacrylate, and polyvinyl acetate.

7. 6. The electrode for a lithium secondary battery according to claim 5, wherein the first insulating layer contains 20% by weight to 99% by weight of a binder.

8. 7. The electrode for a lithium secondary battery according to claim 6, wherein the second insulating layer contains 20% by weight to 99% by weight of a binder.

9. 2. The electrode for a lithium secondary battery according to claim 1, wherein the first insulating layer and the second insulating layer each have a thickness of 1 μm to 15 μm.

10. A method for producing an electrode for a lithium secondary battery according to claim 1, comprising the steps of: preparing an insulating liquid for forming a first insulating layer by mixing a solvent and a binder component including a first binder; preparing an insulating liquid for forming a second insulating layer by mixing inorganic particles, a solvent, and a binder component including a second binder; Applying an electrode mixture slurry containing an electrode active material onto a current collector; and applying the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer.

11. 11. The method of claim 10, wherein the insulating liquid applying step applies the insulating liquid for forming the second insulating layer on a coating layer of the insulating liquid for forming the first insulating layer.

12. 12. The method of claim 11, wherein the insulating liquid application is performed such that a surface of the insulating liquid for forming the first insulating layer is completely covered with the insulating liquid for forming the second insulating layer.

13. The method for producing an electrode for a lithium secondary battery according to claim 11, wherein the viscosity of the insulating liquid for forming the first insulating layer and the insulating liquid for forming the second insulating layer is 1,000 cps to 10,000 cps at 25°C.

14. 14. The method for producing an electrode for a lithium secondary battery according to claim 13, wherein the viscosity of the insulating liquid for forming the second insulating layer is lower than the viscosity of the insulating liquid for forming the first insulating layer.

15. The method for producing an electrode for a lithium secondary battery according to claim 10 , wherein a solvent of the insulating liquid for forming the first insulating layer and a solvent of the insulating liquid for forming the second insulating layer are the same.

16. A lithium secondary battery comprising the electrode for lithium secondary batteries according to claim 1 as a positive electrode or a negative electrode.

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