Positive electrode for lithium secondary battery including insulating layer having excellent wet adhesion and lithium secondary battery including same

Abstract

The present invention relates to a positive electrode for a lithium secondary battery including an insulating layer having excellent wet adhesion and a lithium secondary battery including the same.SOLUTION: Since the insulating layer has excellent wet adhesion in an electrolyte solution, there is an advantage in that it is possible to inhibit the movement of lithium ions in the overlaid region of the electrode, thereby suppressing capacity expression and the like.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0100426, filed July 30, 2021, and Korean Patent Application No. 10-2022-0092191, filed July 26, 2022, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a positive electrode for a lithium secondary battery including an insulating layer with excellent wet adhesion, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0003] With technological development and increasing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing, and as a result, much research is being conducted into batteries that can meet various needs.

[0004] Typically, from the viewpoint of battery shape, there is a high demand for prismatic batteries and pouch-type batteries that are thin and applicable to products such as mobile phones, and from the viewpoint of materials, there is a high demand for lithium secondary batteries such as lithium cobalt polymer batteries that have excellent energy density, discharge voltage, and safety.

[0005] One of the main research topics for secondary batteries is improving their safety. The primary cause of safety-related battery accidents is abnormally high temperatures caused by short circuits between the positive and negative electrodes. Under normal circumstances, a separator between the positive and negative electrodes maintains electrical insulation. However, in abnormal situations, 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 the battery is subjected to excessive deformation due to external force, the conventional separator alone reaches its limits.

[0006] Typically, microporous membranes made of polyolefin resins are used as separators, but their heat resistance is insufficient, with a temperature range of approximately 120°C to 160°C. Therefore, when an internal short circuit occurs, the separator shrinks due to the heat generated by the short circuit reaction, expanding the short circuit area and generating more reaction heat, leading to a thermal runaway condition. This phenomenon primarily occurs at the edges of the electrode active material coating on the electrode current collector when the electrodes are stacked. Therefore, various methods have been attempted to reduce the possibility of electrode short circuits due to external impact or high temperatures.

[0007] Specifically, to solve the internal short circuit of a battery, methods have been proposed, such as attaching insulating tape to the uncoated portion of the electrode and a portion of the active material layer, or coating an insulating liquid to form an insulating layer. For example, methods include applying an insulating binder to the uncoated portion of the positive electrode and a portion of the active material layer, or coating an insulating liquid in which a mixture of the binder and inorganic particles is dispersed in a solvent to form an insulating layer.

[0008] Meanwhile, in actual secondary batteries, electrodes exist in a state where they are immersed in an electrolyte, and conventional insulating layers have a reduced adhesive strength (hereinafter referred to as wet adhesive strength) when immersed in the electrolyte, which means they are unable to prevent lithium ions from migrating to the overlay region of the electrode, resulting in the problem of capacity development (see Figure 1). In particular, lithium ions can precipitate in the overlay region of the electrode when capacity is developed, which can cause a decrease in the stability of the battery cell.

[0009] Therefore, there is a need to develop an insulating layer with excellent wet adhesion. Summary of the Invention [Problem to be solved by the invention]

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a positive electrode for a lithium secondary battery including an insulating layer having excellent wet adhesion, a method for producing the same, and a lithium secondary battery including the same. [Means for solving the problem]

[0011] In one embodiment, the present invention provides a battery comprising a current collector, an active material layer formed on one or both sides of the current collector and including a positive electrode active material, a conductive material, and a non-aqueous binder, and an insulating layer positioned on a side of the active material layer, the insulating layer being formed of an aqueous binder substituted with a non-aqueous solvent.

[0012] In one embodiment, the insulating layer is located on the current collector and has a structure formed to cover a portion of the uncoated portion of the current collector and a portion of the active material layer applied to the current collector.

[0013] In one specific embodiment, the insulating layer is located on the current collector and has a structure formed to cover a portion of the uncoated area of ​​the current collector and a portion of the sliding area of ​​the active material layer applied to the current collector, and the formed height of the insulating layer is within a range of 10 to 50% of the height of the active material layer.

[0014] In another embodiment, the insulating layer is located on the current collector and is formed to cover a portion of the uncoated area of ​​the current collector and a portion of the sliding area of ​​the active material layer applied to the current collector, and the formed height of the insulating layer is within a range of 50 to 100% of the height of the active material layer.

[0015] For example, the thickness of the insulating layer is in the range of 1 μm to 50 μm on average.

[0016] In one embodiment, the insulating layer further comprises inorganic particles dispersed in an aqueous binder substituted with a non-aqueous solvent, and the weight ratio of the inorganic particles to the aqueous binder is in the range of 1:99 to 95:5.

[0017] The inorganic particles may be one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, MgO, CaO, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, ZrO2, BaTiO3, SnO2, CeO2, Y2O3, SiO2, silicon carbide (SiC), and boron nitride (BN).

[0018] Furthermore, the aqueous binder may be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose.

[0019] Furthermore, the non-aqueous binder of the active material layer may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropene (PVDF-co-HFP, Poly(vinylidene fluoride-co-hexafluoropropene)), poly(ethylene oxide) (PEO, Poly(ethylene oxide)), polyacrylic acid (PAA), polyimide (PI), polyamideimide (PAI), and polyimide-polyamideimide copolymer (PI-PAI).

[0020] In a specific example, the non-aqueous binder may be polyvinylidene fluoride (PVDF), and the aqueous binder may be an aqueous binder substituted with a non-aqueous organic solvent, such as styrene-butadiene rubber substituted with N-methyl-2-pyrrolidone solvent.

[0021] Meanwhile, in one embodiment of the present invention, the insulating layer may have a composition containing both an aqueous binder substituted with a non-aqueous solvent and a non-aqueous binder. For example, the insulating layer may have a composition in which the aqueous binder and the non-aqueous binder are mixed in a weight ratio of 20:80 to 80:20, or in a weight ratio of 40:60 to 60:40.

[0022] Furthermore, the present invention provides a lithium secondary battery including the above-described positive electrode for a secondary battery. [Effects of the Invention]

[0023] The positive electrode for a lithium secondary battery including an insulating layer having excellent wet adhesion according to the present invention and a lithium secondary battery including the same have the advantage that the insulating layer has excellent wet adhesion in an electrolyte, thereby preventing the migration of lithium ions in the overlay region of the electrode and suppressing capacity development, etc. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a diagram showing a schematic diagram of lithium ion migration in the overlay region of an electrode. [Figure 2] 1 is a flowchart showing a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention. [Figure 3] FIG. 10 is a diagram showing the results of measuring the wet adhesive strength of insulating layers of an example and a comparative example. [Figure 4] 1 is a graph showing the results of measuring the discharge capacity to evaluate the capacity development of the battery cells of Examples 5 to 7 (room temperature discharge characteristics). [Figure 5] 1 is a graph showing the results of measuring the discharge capacity to evaluate the capacity development of the battery cells of Examples 5 to 7 (high-temperature discharge characteristics). DETAILED DESCRIPTION OF THE INVENTION

[0025] While the present invention may be modified in many ways and may have various embodiments, specific examples will be described in detail in the detailed description.

[0026] However, it should be understood that this is not intended to limit the invention to any particular embodiment, but rather to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0027] In the present invention, the terms "comprise" and "have" are intended to specify the presence of any feature, number, step, operation, component, part, or combination thereof described in the specification, and should be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0028] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion in between. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion in between. Furthermore, in the present application, being "located on" may include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0029] In the present invention, the term "insulating layer" refers to an insulating member formed by applying and drying from at least a portion of the uncoated area of ​​the electrode current collector to at least a portion of the electrode active material layer.

[0030] In the present invention, the term "wet adhesion" refers to the adhesion of an insulating layer measured in a state where the insulating layer is immersed in an electrolyte. More specifically, the wet adhesion can be measured by immersing a metal test piece having an insulating layer formed thereon in an electrolyte, applying ultrasonic waves, and then checking for swelling or detachment of the insulating layer.

[0031] In the present invention, the term "metal test piece" refers to a metal current collector used in the manufacture of an electrode, which is a space where an insulating layer is formed, and may be a metal current collector punched to have a predetermined width and length. For example, the metal test piece may be made of aluminum, copper, or an aluminum alloy.

[0032] In the present invention, the term "overlay region" refers to a region of an electrode where an insulating layer is formed. More specifically, the insulating layer covers from at least a portion of the uncoated portion of an electrode on which an active material layer is formed to at least a portion of the active material layer, and the region of the active material layer on which the insulating layer is formed can be referred to as the overlay region.

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

[0034] <Positive electrodes for lithium secondary batteries> In one embodiment, the present invention includes a current collector; an active material layer formed on one or both surfaces of the current collector and including a positive electrode active material, a conductive material, and a non-aqueous binder; and an insulating layer located on a side surface of the active material layer.

[0035] The insulating layer is formed of an aqueous binder substituted with a non-aqueous solvent. In the present invention, by using an aqueous binder when forming the insulating layer, wet adhesion strength can be increased, and the insulating layer can be stably applied to a positive electrode that is vulnerable to moisture through the substitution of the non-aqueous solvent.

[0036] The secondary battery electrode according to the present invention has an advantage that it includes an insulating layer having excellent wet adhesion and can inhibit the migration of lithium ions in the overlay region of the electrode, thereby suppressing the development of capacity.

[0037] Generally, the positive electrode in a secondary battery is impregnated with an electrolyte. However, conventional insulating layers have poor wet adhesion when impregnated with the electrolyte, preventing lithium ion migration to the overlay region of the positive electrode, resulting in a problem of capacity development. In particular, lithium ions can precipitate in the overlay region of the positive electrode during capacity development, resulting in reduced stability of the battery cell. In the present invention, during the fabrication of the positive electrode of a secondary battery, an insulating layer is formed using an aqueous binder substituted with the same non-aqueous solvent as the solvent of the positive electrode slurry, thereby preventing gelation due to differences in the type of binder between the active material layer and the coating layer. In particular, the insulating layer dries simultaneously with the solvent of the positive electrode slurry during the drying process, preventing cracking between the active material layer and the insulating layer due to differences in drying speed or temperature.

[0038] Furthermore, the insulating layer further contains inorganic particles, which has the effect of improving electrical insulation and thermal stability and suppressing thermal expansion.

[0039] Meanwhile, the wet adhesion strength of the insulating layer can be measured by immersing a metal test piece on which an insulating layer has been formed in an electrolyte, applying ultrasonic waves, and then checking whether or not the insulating layer formed on the metal test piece has swelled or detached.

[0040] The electrolyte solution used in measuring the wet adhesive strength may contain an organic solvent and an electrolyte salt, and the electrolyte salt may be a lithium salt. The lithium salt may be any of those commonly used in non-aqueous electrolytes for lithium secondary batteries. For example, the anion of the lithium salt may be F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 -, (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - It may contain any one or two or more selected from the group consisting of:

[0041] The organic solvent contained in the electrolyte solution may be any organic solvent commonly used in electrolyte solutions for lithium secondary batteries, and may be any of ethers, esters, amides, linear carbonates, cyclic carbonates, etc., which may be used alone or in combination of two or more. Among these, representative examples include carbonate compounds such as cyclic carbonates, linear carbonates, and mixtures thereof.

[0042] In the positive electrode for a lithium secondary battery according to the present invention, the insulating layer may contain a water-based binder.

[0043] In a specific example, the aqueous binder may be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose. In a specific example, the aqueous binder may be one or more selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, and acrylonitrile-butadiene-styrene rubber. For example, the aqueous binder may be styrene-butadiene rubber.

[0044] Conventionally, polyvinylidene fluoride (PVDF) has been used as a binder for the insulating layer of a positive electrode, but this has the problem of reduced wet adhesion when immersed in an electrolyte. Therefore, in the present invention, styrene-butadiene rubber can be used as the binder polymer. When styrene-butadiene rubber is used as the polymer binder, water can be used as the solvent. However, in this case, gelation can occur between the insulating composition and the positive electrode slurry due to the difference in the type of binder when the insulating composition and the positive electrode slurry are simultaneously coated.

[0045] In a specific example, the aqueous binder may be an aqueous binder substituted with a non-aqueous organic solvent. Here, the non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone, methyl alcohol, ethyl alcohol, and isopropyl alcohol.

[0046] For example, the aqueous binder may be styrene-butadiene rubber substituted with NMP solvent. More specifically, the insulating layer may be formed by applying an insulating composition to cover at least a portion of the uncoated area and at least a portion of the active material layer, and then drying the composition at a temperature of about 50 to 300°C. In this case, the insulating layer may be formed by removing the solvent during the drying process, and the styrene-butadiene rubber dispersed in the solvent may be replaced with the NMP-substituted styrene-butadiene rubber.

[0047] Furthermore, the insulating layer may contain inorganic particles, which can improve the safety of the battery and the strength of the insulating layer. The content of the inorganic particles may be appropriately adjusted taking into consideration the viscosity, thermal resistance, insulating properties, filling effect, dispersibility, or stability of the insulating composition. Generally, the larger the size of the inorganic particles, the higher the viscosity of the composition containing them and the greater the likelihood of sedimentation in the insulating composition. Furthermore, the smaller the size of the inorganic particles, the higher the thermal resistance tends to be. Therefore, the appropriate type and size of inorganic particles may be selected taking these factors into consideration, and two or more types of inorganic particles may be used together if necessary.

[0048] In a specific example, the inorganic particles of the insulating layer may be one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, Al(OH)3, Mg(OH)2, Ti(OH)4, MgO, CaO, Cr2O3, MnO2, Fe2O3, Co3O4, NiO, ZrO2, BaTiO3, SnO2, CeO2, YO3, SiO2, silicon carbide (SiC), and boron nitride (BN), or one or more selected from the group consisting of AlOOH, Al2O3, γ-AlOOH, and Al(OH)3. For example, the inorganic particles may be AlOOH.

[0049] The weight ratio of the inorganic particles to the aqueous binder may be within the range of 1:99 to 95:5, 10:90 to 70:30, 20:80 to 60:40, or 40:60 to 60:40. For example, the weight ratio of the inorganic particles to the aqueous binder in the insulating composition may be 50:50. On the other hand, if the content of the aqueous binder is too low, it may be difficult to achieve the desired insulating effect in the present invention, and the adhesive strength with the electrode may be weakened. Furthermore, if the content of the aqueous binder is too high, the insulating composition may flow in the overlay region when coating the electrode, resulting in a decrease in the safety of the battery cell.

[0050] The inorganic particles may have an average particle size of 0.1 μm to 100 μm, 0.5 μm to 80 μm, 1 μm to 50 μm, 2 μm to 30 μm, 3 μm to 20 μm, or 5 μm to 10 μm. If the size of the inorganic particles is within the above range, they cannot be uniformly coated on the electrode, minimizing the resistance of lithium ions and ensuring the performance of the lithium secondary battery.

[0051] In another example, the insulating composition may include first and second inorganic particles having different particle size balances and a bimodal particle size distribution. This means that the inorganic particles are a mixture of small and large particles, and an appropriate amount of inorganic particles may be dispersed so that the empty spaces between the large first inorganic particles can be filled with the small second inorganic particles. However, this is not limited to this.

[0052] On the other hand, the thickness of the insulating layer is set within a range of 0.2 μm to 100 μm, and may be specifically 1 μm to 50 μm, more specifically 1 μm to 30 μm, 2 μm to 30 μm, 3 μm to 20 μm, or 5 μm to 15 μm. If the thickness of the coating portion is too thin, it may be difficult to expect the effect of applying the insulating layer to improve safety.

[0053] Furthermore, the active material layer may include a positive electrode active material. In a specific example, the positive electrode active material may be any commonly used positive electrode active material, such as, but not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a lithium composite oxide formed by combining these.

[0054] The content of the positive electrode active material may be 85 to 95 parts by weight, specifically 88 to 95 parts by weight, 90 to 95 parts by weight, 86 to 90 parts by weight, or 92 to 95 parts by weight, per 100 parts by weight of the active material layer.

[0055] In this case, the conductive material can be used to improve the performance of the positive electrode, such as electrical conductivity, and can be at least one material selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber. For example, the conductive material may include acetylene black.

[0056] The conductive material may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 2 to 6 parts by weight, relative to 100 parts by weight of the active material layer.

[0057] Furthermore, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. As an example, the binder may include polyvinylidene fluoride.

[0058] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 2 to 6 parts by weight, relative to 100 parts by weight of the entire active material layer.

[0059] Furthermore, the average thickness of the active material layer is not particularly limited, but may specifically be 10 μm to 500 μm or 50 μm to 400 μm, and more specifically may be 50 μm to 350 μm, 100 μm to 400 μm, 100 μm to 400 μm, 200 μm to 300 μm, or 50 μm to 250 μm.

[0060] Meanwhile, the positive electrode for a lithium secondary battery according to the present invention can use a current collector that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used. In the case of aluminum or stainless steel, it is also possible to use a current collector that has been surface-treated with carbon, nickel, titanium, silver, etc. In addition, the current collector can be formed with fine irregularities on its surface to enhance the adhesion of the positive electrode active material, and can be in various forms such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. Furthermore, the average thickness of the current collector can be appropriately set to 3 to 500 μm, taking into account the conductivity and total thickness of the positive electrode to be manufactured.

[0061] <Method of manufacturing a positive electrode for a lithium secondary battery> In one embodiment, the present invention includes the steps of: applying a positive electrode slurry containing a positive electrode active material, a conductive material, and a non-aqueous binder to one or both surfaces of a current collector; applying an insulating composition containing an aqueous binder substituted with a non-aqueous solvent from at least a portion of an uncoated portion of the current collector to cover a portion of the positive electrode slurry applied to the current collector; and drying the positive electrode slurry and insulating composition applied to the current collector. The positive electrode slurry and insulating composition each contain the same non-aqueous solvent.

[0062] FIG. 2 is a flowchart illustrating a method for manufacturing a positive electrode for a lithium secondary battery according to the present invention. Referring to FIG. 2, the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention includes coating a positive electrode slurry on one or both sides of a current collector, and coating an insulating composition on at least a portion of the uncoated area of ​​the current collector to cover a portion of the positive electrode slurry coated on the current collector. Meanwhile, the insulating composition may be applied to the wet positive electrode slurry. Here, "wet" refers to a slurry that has not undergone a separate drying process using a drying device or equipment. The present invention may also include a step of drying the positive electrode slurry and insulating composition coated on the current collector. In particular, according to the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, the positive electrode slurry and insulating composition coated on the current collector are simultaneously dried to increase the adhesion between the positive electrode active material and the insulating layer, thereby reducing interfacial resistance and forming a dense insulating layer that is resistant to mechanical properties such as breakage. Furthermore, the efficiency of the positive electrode manufacturing process can be improved.

[0063] In the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, the positive electrode slurry and the insulating composition each contain the same non-aqueous organic solvent. When the positive electrode slurry and the insulating composition each contain the same solvent, problems such as gelation of different binders and cracking during drying due to differences in boiling points can be resolved.

[0064] The non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma-butyrolactone, methyl alcohol, ethyl alcohol, and isopropyl alcohol.

[0065] In a specific example, the non-aqueous organic solvent may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC) and dimethyl sulfoxide (DMSO), or may be one or more selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF) and dimethylacetamide (DMAc).

[0066] For example, the non-aqueous organic solvent may be an amide-based organic solvent, and the same solvent as that used in preparing the positive electrode slurry may be used. The non-aqueous organic solvent may be N-methyl-pyrrolidone (NMP).

[0067] When NMP is used as the solvent for the positive electrode slurry, the solvent for the insulating composition may also be NMP. In particular, using NMP as the solvent for the insulating composition can prevent cracks from occurring at the boundary between the insulating coating and the active material layer in the overlay region of the electrode. The insulating composition for a secondary battery electrode according to the present invention can be coated and dried simultaneously with the positive electrode slurry. In particular, NMP can be used as a substitution solvent during the drying process.

[0068] Hereinafter, the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention will be described in detail.

[0069] Step S10: Coating one or both surfaces of a current collector with a positive electrode slurry. The method for manufacturing a positive electrode for a lithium secondary battery according to the present invention includes the step of coating a positive electrode slurry on one or both surfaces of a current collector.

[0070] In this case, the positive electrode for a lithium secondary battery according to the present invention can use a current collector that has high conductivity without inducing chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, etc. can be used. In the case of aluminum or stainless steel, it can also be surface-treated with carbon, nickel, titanium, silver, etc. For example, the current collector can be aluminum.

[0071] Furthermore, in the slurry for the positive electrode active material, any positive electrode active material commonly used in positive electrodes can be used as the positive electrode active material, and examples thereof that can be used include, but are not limited to, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, and lithium composite oxides combining these.

[0072] The non-aqueous binder contained in the positive electrode active material slurry may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0073] In this case, the conductive material can be used to improve the performance of the positive electrode, such as electrical conductivity, and can be at least one material selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, and carbon fiber. For example, the conductive material may include acetylene black.

[0074] Furthermore, the solvent used in the positive electrode slurry may be one or more non-aqueous organic solvents selected from the group consisting of N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate (BC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), acetonitrile, dimethoxyethane, tetrahydrofuran (THF), gamma butyrolactone, methyl alcohol, ethyl alcohol, and isopropyl alcohol, and may be, for example, N-methyl-2-pyrrolidone (NMP).

[0075] Step (S20) of applying an insulating composition to at least a portion of the uncoated portion of the current collector so as to cover a portion of the positive electrode slurry applied to the current collector.

[0076] In the method for manufacturing a positive electrode for a lithium secondary battery according to the present invention, an insulating composition including inorganic particles and an aqueous binder may be applied to at least a portion of an uncoated portion of the current collector to cover a portion of the positive electrode slurry applied to the current collector.

[0077] In this case, the positive electrode slurry may be in an undried state, where "undried" means a slurry that has not undergone a separate drying process using a drying device or equipment.

[0078] In this case, the insulating composition contains inorganic particles and a water-based binder, which can provide excellent wet adhesion, thereby suppressing the migration of lithium ions in the overlay region of the positive electrode and preventing the precipitation of lithium ions.

[0079] <Lithium secondary battery> In one embodiment, the present invention provides a lithium secondary battery including the positive electrode for a lithium secondary battery according to the present invention. The lithium secondary battery according to the present invention may include the positive electrode of the present invention, an anode, and a separator disposed between the positive electrode and the anode.

[0080] In particular, the lithium secondary battery according to the present invention has an advantage that the insulating layer has excellent wet adhesion in the electrolyte, thereby preventing the migration of lithium ions in the overlay region of the electrode and suppressing capacity development, etc. As a result, the lithium secondary battery according to the present invention can have improved stability.

[0081] Here, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector and containing a negative electrode active material. Specifically, the negative electrode is manufactured by applying, drying, and pressing a negative electrode active material on a negative electrode current collector, and may further selectively contain a conductive material, an organic binder polymer, a filler, etc. as described above as necessary.

[0082] In addition, the negative electrode active material includes, for example, graphite having a complete layered crystal structure such as natural graphite, soft carbon having a low-crystalline layered crystal structure (graphene structure; a structure in which hexagonal honeycomb-shaped planes of carbon are arranged in layers), and hard carbon in which such a structure is mixed with an amorphous portion, artificial graphite, expanded graphite, carbon fiber, graphitization-resistant carbon, carbon black, carbon nanotube, fullerene, activated carbon, and other carbon and graphite materials; 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; titanium oxides; lithium titanium oxides, etc. can be used.

[0083] For example, the negative electrode active material may include both graphite and silicon (Si)-containing particles, and the graphite may include at least one of natural graphite having a layered crystal structure and artificial graphite having an isotropic structure. The silicon (Si)-containing particles are particles containing silicon (Si) as a metal component as a main component, and may include silicon (Si) particles, silicon oxide (SiO2) particles, or a mixture of the silicon (Si) particles and silicon oxide (SiO2) particles.

[0084] In this case, the negative electrode active material may contain 80 to 95 parts by weight of graphite and 1 to 20 parts by weight of silicon (Si)-containing particles, based on a total of 100 parts by weight. By adjusting the contents of graphite and silicon (Si)-containing particles in the negative electrode active material within the above ranges, the present invention can reduce lithium consumption and irreversible capacity loss during initial charge / discharge of the battery, and improve charge capacity per unit mass.

[0085] The negative electrode active material layer may have an average thickness of 100 μm to 200 μm, specifically, 100 μm to 180 μm, 100 μm to 150 μm, 120 μm to 200 μm, 140 μm to 200 μm, or 140 μm to 160 μm.

[0086] Furthermore, the negative electrode current collector is not particularly limited as long as it does not induce chemical changes in the battery and has high conductivity. For example, copper, stainless steel, nickel, titanium, baked carbon, etc. can be used. In the case of copper or stainless steel, those surface-treated with carbon, nickel, titanium, silver, etc. can also be used.

[0087] Similarly to the positive electrode current collector, the negative electrode current collector may have fine irregularities on its surface to strengthen the bonding force with the negative electrode active material, and may be in various forms such as a film, sheet, foil, net, porous body, foam, nonwoven fabric, etc. Furthermore, the average thickness of the negative electrode current collector may be appropriately set to 3 to 500 μm, taking into consideration the conductivity and total thickness of the negative electrode to be manufactured.

[0088] The separator is an insulating thin film interposed between the positive and negative electrodes and exhibits high ion permeability and mechanical strength. The separator may be any material commonly used in the art, including sheets or nonwoven fabrics made of chemically resistant and hydrophobic polypropylene, glass fiber, or polyethylene. In some cases, composite separators may be used, in which inorganic particles or organic particles are coated with an organic binder polymer on a porous polymer substrate such as the above-mentioned sheets or nonwoven fabrics. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as the separator. The separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0089] Meanwhile, the positive electrode and the negative electrode may be wound in a jelly roll form and housed in a cylindrical battery, a prismatic battery, or a pouch battery, or may be housed in a folded or stack-and-folded form in a pouch battery, but are not limited thereto.

[0090] The lithium salt-containing electrolyte solution according to the present invention may be composed of an electrolyte solution and a lithium salt, and the electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, or the like.

[0091] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0092] Examples of the organic solid electrolyte that can be used include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyagitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polymerizing agents containing ionic dissociative groups.

[0093] Examples of the inorganic solid electrolyte that can be used include nitrides, halides, and sulfates of Li, such as LiN, LiI, LiNi, LiN-LiI-LiOH, LiSiO, LiSiO-LiI-LiOH, LiSiS, LiSiO, LiSiO-LiI-LiOH, and LiPO-LiS-SiS.

[0094] The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte, and examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, and LiB 10 Cl 10 , LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylates, lithium 4-phenylboronate, imides, etc. can be used.

[0095] In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., the electrolyte may contain, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, etc. In some cases, to impart non-flammability, a halogen-containing solvent such as carbon tetrachloride or trifluoroethylene may be further added, and to improve high-temperature storage characteristics, carbon dioxide gas may be further added, or FEC (fluoroethylene carbonate), PRS (propene sultone), etc. may be further added.

[0096] Meanwhile, in one embodiment, the present invention provides a battery module including the above-described secondary battery as a unit battery, and a battery pack including the battery module.

[0097] The battery pack can be used as a power source for medium- to large-sized devices that require high-temperature stability, long cycle characteristics, and high rate characteristics. Specific examples of such medium- to large-sized devices include power tools powered by electric motors; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); electric two-wheeled vehicles, including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems, more specifically, hybrid electric vehicles (HEVs) are included, but are not limited to these.

[0098] Furthermore, the positive electrode and the negative electrode may be wound in a jelly roll shape and housed in a cylindrical battery, a prismatic battery, or a pouch battery, or may be housed in a folded or stack-and-folded form in a pouch battery. For example, the lithium secondary battery according to the present invention may be a pouch battery.

[0099] As described above, the lithium secondary battery including the cathode active material according to the present invention can be used in a battery module or battery pack including a plurality of unit batteries. Specifically, the lithium secondary battery is useful in portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0100] The present invention will be described in more detail below based on examples and experimental examples.

[0101] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0102] Example 1 To 100g of styrene-butadiene rubber (SBR) (ZEON Corporation, BM451B product) dispersed in water at a 60:40 weight ratio, 500g of N-methyl-2-pyrrolidone (NMP) solvent was added and stirred. The stirred mixture was then heated at 100-120°C for 2 hours to completely evaporate the water, producing an NMP-substituted SBR binder. The NMP-substituted SBR binder and inorganic particles were then mixed and stirred in a 50:50 weight ratio to produce an insulating composition. The resulting insulating composition had a viscosity of 5,000 cP.

[0103] <Examples 2 to 4, Comparative Examples 1 and 2> An insulating coating solution was obtained in the same manner as in Example 1, except that the contents of inorganic particles and binder were changed when preparing the insulating composition.

[0104] The specific compositions of Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1 below.

[0105] [Table 1]

[0106] <Experimental Example 1. Measurement of wet adhesive strength of insulating layer> In order to evaluate the adhesive strength of the insulating layer according to the present invention, the following experiment was carried out.

[0107] Metal test piece with an insulating layer The insulating compositions produced in Examples 1 to 4 and Comparative Examples 1 and 2 were coated on aluminum metal foil and dried to prepare metal test pieces with an insulating layer of approximately 10 μm in thickness. The metal test pieces with the insulating layer formed thereon were punched out to a size of 2 cm × 2 cm using a punching machine for adhesive strength measurement.

[0108] Ultrasonic application 200 g of an electrolytic solution (EC / EMC = 3 / 7 (vol.%)) was placed in a 250 ml beaker, and the metal test piece with the insulating layer formed thereon was impregnated with the electrolytic solution. The metal test piece was fixed in a jig to control its movement.

[0109] In addition, ultrasonic waves were applied to the electrolyte solution in which the metal test pieces were impregnated using an ultrasonic disperser (BANDELIN, 4200) under the following conditions for applying ultrasonic waves. - Frequency: 20kHz - Tip diameter: 13mm (TS-113) - Amplitude: 100% (Peak-to-peak interval: 132 μm when using a 13 mm tip)

[0110] The results are shown in Table 2 below and in FIG.

[0111] [Table 2]

[0112] Figure 3 shows the results of measuring the wet adhesion strength of the insulating layers of Examples 1 and 4 and Comparative Examples 1 and 2. Table 2 and Figure 2 show that the insulating layer of the electrode specimen of Example 1 did not experience swelling or detachment. However, in the case of Example 1, the boiling point of EMC was 107.5°C due to the increase in temperature of the electrolyte caused by the application of ultrasound. The solvent evaporated, changing the measurement environment, and the measurement was stopped when the temperature reached 109°C.

[0113] Furthermore, in the cases of Examples 2 and 3, although not shown in the photographs, no swelling or detachment occurred in the insulating layer of the electrode test piece, as in Example 1. However, the boiling point of EMC is 107.5°C, and the solvent evaporated, changing the measurement environment, and the measurement was stopped when it reached 109°C.

[0114] In Example 4, no swelling or detachment of the electrode specimen occurred within 15 minutes after ultrasonic waves were applied to the electrolyte. However, although not shown, swelling and detachment of the electrode specimen occurred when the temperature of the electrolyte increased to 108°C due to the continued application of ultrasonic waves.

[0115] Furthermore, in the case of Comparative Examples 1 and 2, swelling and detachment occurred in the electrode test pieces 5 minutes after ultrasonic waves were applied to the electrolyte solution.

[0116] This confirmed that the insulating layer of the example had superior wet adhesion strength compared to the insulating layers of comparative examples 1 and 2.

[0117] <Experimental Example 2. Evaluation of battery cell capacity development> To evaluate the performance of the positive electrode including the insulating layer according to the present invention, a half cell was prepared and then the capacity development was evaluated.

[0118] Half-cell fabrication LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 A positive electrode slurry was prepared by weighing 96 parts by weight of O2, 2 parts by weight of PVDF as a binder, and 2 parts by weight of carbon black as a conductive material in an N-methylpyrrolidone (NMP) solvent. The active material layer slurry was applied to aluminum foil, dried, and then rolled to prepare a positive electrode having a positive electrode active material layer (average thickness: 130 μm).

[0119] The positive electrode was then dip-coated with the insulating coating solution obtained in Examples 1 to 3 and dried in a convection oven (130°C) to form an insulating layer with a thickness of 10 μm on the positive electrode. A coin-shaped half cell was fabricated using lithium foil as the negative electrode and an electrolyte solution containing 1M LiPF6 in a solvent of EC:DMC:DEC = 1:2:1.

[0120] [Table 3]

[0121] Discharge capacity measurement The discharge characteristics of the batteries of Examples 5 to 7 were evaluated under the following conditions: The discharge characteristics were measured at room temperature (25°C) and at a high temperature (45°C). - Discharge: 0.1C, 0.33C, 0.5C, 1.0C, 2.5V cutoff

[0122] On the other hand, in order to compare whether or not each battery exhibited capacity, a battery cell including an electrode on which no insulating layer was formed was used as Comparative Example 3. The results are shown in Table 4 and Fig. 4, and Table 5 and Fig. 5.

[0123] [Table 4]

[0124] [Table 5]

[0125] Referring to Tables 4 and 5 and Figures 4 and 5, it was confirmed that in the case of Example 7, a portion of the capacity was developed during 0.1 C discharge at high temperature (45°C), but the batteries of Examples 5 and 6 hardly developed any capacity during room temperature discharge (25°C).

[0126] These results suggest that the insulating layer has excellent wet adhesion in the electrolyte, preventing the migration of lithium ions in the overlay region of the electrode and suppressing the development of capacity during discharge. As a result, the lithium secondary battery according to the present invention is expected to be able to suppress capacity degradation due to increased cycles and improve safety.

[0127] Although the present invention has been described above with reference to preferred embodiments, it will be understood that a person skilled in the art or with ordinary knowledge in the art can make various modifications and changes to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0128] Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

Claims

1. A current collector; an active material layer formed on one or both surfaces of the current collector and containing a positive electrode active material, a conductive material, and a non-aqueous binder; an insulating layer located on a side surface of the active material layer, The positive electrode for a lithium secondary battery, wherein the insulating layer is made of an aqueous binder substituted with a non-aqueous solvent.

2. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the insulating layer is located on the current collector and covers a portion of an uncoated portion of the current collector and a portion of an active material layer coated on the current collector.

3. the insulating layer is positioned on the current collector and covers a portion of the uncoated area of ​​the current collector and a portion of the sliding area of ​​the active material layer applied to the current collector; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the height of the insulating layer is within a range of 10 to 50% of the height of the active material layer.

4. the insulating layer is positioned on the current collector and covers a portion of the uncoated area of ​​the current collector and a portion of the sliding area of ​​the active material layer applied to the current collector; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the height of the insulating layer is within a range of 50 to 100% of the height of the active material layer.

5. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the insulating layer has an average thickness in the range of 1 μm to 50 μm.

6. the insulating layer further comprises inorganic particles dispersed in an aqueous binder substituted with a non-aqueous solvent; 2. The positive electrode for a lithium secondary battery according to claim 1, wherein a weight ratio of the inorganic particles to the aqueous binder is in the range of 1:99 to 95:

5.

7. The inorganic particles include AlOOH, Al ２ O ３ , γ-AlOOH, Al(OH) ３ , Mg(OH) ２ , Ti(OH) ４ , MgO, CaO, Cr ２ O ３ , MnO ２ , Fe ２ O ３ , Co ３ O ４ , NiO, ZrO ２ , BaTiO ３ , SnO ２ , CeO ２ , Y ２ O ３ , SiO ２ 7. The positive electrode for a lithium secondary battery according to claim 6, wherein the material is at least one selected from the group consisting of silicon carbide (SiC) and boron nitride (BN).

8. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the aqueous binder is at least one selected from the group consisting of styrene-butadiene rubber, acrylate styrene-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, hydroxypropyl methylcellulose, hydroxypropyl cellulose, and diacetyl cellulose.

9. 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the non-aqueous binder is at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropene (PVDF-co-HFP), polyacrylic acid (PAA), polyimide (PI), polyamideimide (PAI), and polyimide-polyamideimide copolymer (PI-PAI).

10. the non-aqueous binder is polyvinylidene fluoride (PVDF); 2. The positive electrode for a lithium secondary battery according to claim 1, wherein the water-based binder is a styrene-butadiene rubber substituted with N-methyl-2-pyrrolidone.

11. A lithium secondary battery comprising the positive electrode for lithium secondary batteries according to claim 1 .

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