Positive electrode and secondary battery comprising the same

Abstract

The positive electrode of the present invention comprises: a current collector, a positive electrode mixture layer provided on a part of the current collector and comprising a positive electrode active material, and an insulating layer provided on the current collector on which the positive electrode mixture layer is not provided, adjacent to the positive electrode mixture layer, wherein the insulating layer comprises a non-aqueous binder comprising a solution-polymerized conjugated diene-based copolymer and inorganic particles, so that cracking can be prevented in the area where the insulating layer and the positive electrode mixture layer overlap each other, and the problems of electrode peeling and insulating layer depression can be solved.

Description

Technical Field

[0001] This specification relates to a positive electrode and a secondary battery comprising the positive electrode, and more specifically, discloses techniques relating to a positive electrode and a secondary battery comprising the positive electrode, which are equipped with a non-aqueous binder comprising a solution-polymerized conjugated diene copolymer and an insulating layer comprising inorganic particles. Background Technology

[0002] In recent years, with technological advancements and the increasing demand for mobile devices, the demand for secondary batteries as an energy source has grown rapidly. Consequently, various studies have been conducted on batteries that can meet diverse needs. In particular, research has been actively pursued on secondary batteries with high energy density and excellent lifespan and cycle characteristics for use as power sources in devices.

[0003] A secondary battery includes a positive electrode containing a positive electrode active material capable of intercalating / deintercalating lithium ions, a negative electrode containing a negative electrode active material capable of intercalating / deintercalating lithium ions, a separator sandwiched between the positive and negative electrodes, and an electrolyte. The positive and negative electrodes have a structure in which an electrode active material layer is formed on one surface of the electrode current collector or on the positive electrode. Recently, to improve electrode stability, a technology for forming an insulating layer on the outer edge of the electrode active material layer is being developed. By forming an insulating layer on the outer edge of the electrode active material layer, the electrode active material layer can be protected from the heat generated during electrode operation, and the insulation between the electrodes can be enhanced.

[0004] Typical electrode insulating layers are usually formed using adhesives with insulating properties. However, due to the weak heat resistance of the adhesives, typical insulating layers made from these adhesives suffer from the following problem: as the battery is driven, the adhesion decreases under high-temperature conditions, thus reducing battery safety. To address these issues, a technique has been proposed to improve the heat resistance of the insulating layer by adding inorganic particles to the coating composition for electrode insulation.

[0005] Even if inorganic particles are added as described above to improve the heat resistance of the insulation layer, an adhesive must still be included, and the insulation coating must be performed using a commonly used non-aqueous adhesive (such as PVDF). However, insulation layers formed with non-aqueous adhesives have the following problem: when impregnated with electrolyte, the adhesion (hereinafter referred to as wet adhesion) decreases, thus affecting capacity due to the inability to prevent the migration of lithium ions to the overlapping areas of the electrodes.

[0006] Therefore, the use of aqueous adhesives, such as emulsion-polymerized styrene-butadiene rubber (SBR), as the insulating layer for electrodes has been investigated. To form the insulating layer using aqueous adhesives, water is used as a solvent during the preparation of the coating solution. However, in the case of electrodes, particularly the positive electrode, there is a limitation that the active material components are extremely sensitive to moisture. Therefore, using water as a solvent may damage the positive electrode active material layer. Furthermore, when the insulating composition used to form the insulating layer contains an aqueous adhesive, there is a limitation that gelation may occur due to contact with non-aqueous adhesives contained in the active material slurry. Summary of the Invention

[0007] Technical issues

[0008] This specification aims to provide a positive electrode in which a solution-polymerized conjugated diene copolymer is used as a binder for the insulating layer, thereby preventing cracking or denting in the overlap between the insulating layer and the positive electrode mixture layer, and preventing the positive electrode mixture layer from peeling off.

[0009] Furthermore, this specification also aims to provide a secondary battery comprising a positive electrode equipped with the aforementioned insulating layer, which, since the insulating layer does not peel off even in an electrolyte-immersed environment, prevents short circuits between electrodes and thus provides improved safety.

[0010] Technical solution

[0011] [1] In one aspect, a positive electrode is provided, comprising: a current collector, a positive electrode mixture layer disposed on a portion of the current collector and comprising a positive electrode active material, and an insulating layer adjacent to the positive electrode mixture layer and disposed on a current collector where the positive electrode mixture layer is not disposed, wherein the insulating layer comprises an adhesive comprising a solution-polymerized conjugated diene copolymer and inorganic particles.

[0012] [2] In the above [1], the solution-polymerized conjugated diene copolymer may contain 5% to 95% by weight diene monomer units and 5% to 95% by weight aromatic vinyl monomer units.

[0013] [3] In [1] and / or [2] above, the adhesive may be free of surfactant.

[0014] [4] In any one or more of [1] to [3] above, the insulating layer may include an overlap covering a portion of the positive electrode mixture layer in the portion that contacts the positive electrode mixture layer.

[0015] [5] In any one or more of [1] to [4] above, the inorganic particles may contain one or more of the group consisting of boehmite (AlOOH), aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3) and zirconium oxide (ZrO2).

[0016] [6] In any one or more of [1] to [5] above, the positive electrode active material may contain a lithium metal phosphate compound, which may be represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-y M y ]PO4 In the above chemical formula 1, M includes one or more of the group consisting of Mn, Co, Ni, Al, Mg and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0017] [7] In any one or more of [1] to [6] above, based on 100 parts by weight of the insulating layer, the insulating layer may contain 40 to 95 parts by weight of the inorganic particles and 5 to 60 parts by weight of the adhesive.

[0018] [8] In any one or more of [1] to [7] above, the adhesive may further comprise an auxiliary adhesive, which may comprise polyvinylidene fluoride.

[0019] [9] In any one or more of [1] to [8] above, the weight ratio of the solution-polymerized conjugated diene copolymer to the auxiliary adhesive may be 95:5 to 70:30.

[0020]

[10] In any one or more of [1] to [9] above, the positive electrode mixture layer may further comprise an adhesive and a conductive material.

[0021]

[11] In one aspect, a method for manufacturing a positive electrode is provided, the method comprising: (S1a) coating a positive electrode slurry comprising a positive electrode active material onto a portion of a current collector; (S1b) coating an insulating coating composition onto a current collector in a region adjacent to the region coated with the positive electrode slurry and in a region not coated with the positive electrode slurry; and (S2) drying the positive electrode slurry and the insulating coating composition coated on the current collector to form a positive electrode mixture layer and an insulating layer, wherein the insulating coating composition comprises a non-aqueous binder containing a solution-polymerized conjugated diene copolymer, a non-aqueous organic solvent, and inorganic particles.

[0022]

[12] In the above

[11] , steps S1a and S1b can be performed before step S2, and can be performed simultaneously or sequentially.

[0023]

[13] In the above

[11] and / or

[12] , the solid content of the positive electrode slurry may be from 50% to 70% by weight, and the solid content of the insulating coating composition may be from 10% to 40% by weight.

[0024]

[14] In one aspect, a secondary battery comprising the above-described positive electrode is provided.

[0025] Beneficial effects

[0026] The positive electrode disclosed in this specification can prevent cracking and denting in the area where the insulating layer and the positive electrode mixture layer overlap.

[0027] The positive electrode manufacturing method disclosed in this specification contains a solution-polymerized conjugated diene copolymer in the insulating coating composition, which prevents the interaction between the positive electrode slurry and the insulating coating composition when coated on the current collector, thereby preventing the positive electrode mixture layer from peeling off or lifting from the positive electrode after the drying step of forming the insulating layer.

[0028] The secondary battery disclosed in this specification exhibits excellent wet adhesion of the insulating layer, thereby maintaining adhesion between the current collector and the positive electrode mixture layer even after electrolyte immersion, thus preventing peeling problems. As a result, this secondary battery improves safety by significantly reducing the possibility of short circuits between electrodes. Attached Figure Description

[0029] Figure 1 A photograph showing the portion of the positive electrode mixture layer and the insulating layer of the electrode in Example 1 that are adjacent to each other.

[0030] Figure 2 A photograph showing a cross-section of the portion of the electrode in Example 1 where the positive electrode mixture layer and the insulating layer are adjacent to each other.

[0031] Figure 3 A photograph showing the portion of the positive electrode mixture layer and the insulating layer of the electrode in Comparative Example 1 that are adjacent to each other.

[0032] Figure 4 A photograph showing a cross-section of the portion of the electrode in Example 1 where the positive electrode mixture layer and the insulating layer are adjacent to each other. Detailed Implementation

[0033] By reference and appendix Figure 1The advantages, features, and implementation methods of the invention described herein will become clear from the following detailed description of the embodiments. However, the invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to make this disclosure fully complete and to fully convey the scope of the invention to those skilled in the art. Furthermore, the invention is defined only by the scope of the claims. Throughout this specification, the same reference numerals refer to the same elements.

[0034] Unless otherwise defined, all terms used herein (including technical and scientific terms) are used in the sense that would be commonly understood by one of ordinary skill in the art to which the inventive concept pertains. Furthermore, unless specifically defined, terms as defined in common dictionaries should not be idealized or over-interpreted.

[0035] The terminology used herein is for descriptive purposes and is not intended to limit the inventive concept. In this specification, the singular includes the plural unless the context clearly indicates otherwise. The terms "comprising" and / or "including" as used herein are intended to cover the stated elements and do not exclude the possibility of the presence or addition of more than one other element.

[0036] In this specification, when a section is referred to as containing a certain element, unless otherwise stated, it means that the section may also contain other elements, rather than not containing other elements.

[0037] In this specification, the description of "A and / or B" means A or B, or A and B.

[0038] In this specification, unless otherwise stated, "%" refers to weight.

[0039] In this specification, D 50 D refers to the particle size corresponding to 50% of the cumulative volume in the particle size distribution curve. 90 This refers to the particle size corresponding to the cumulative 90% of the particle size distribution curve. (D) 50 and D 90 Laser diffraction, for example, can be used for measurement. Laser diffraction can typically measure particle sizes from submicron to several millimeters, thus providing highly reproducible and high-resolution results.

[0040] In this specification, the positive electrode, the method for manufacturing the positive electrode, and the secondary battery containing the positive electrode each include one or more of the following technical features and / or technical configurations, and these technical features and / or technical configurations can be combined in various ways.

[0041] The following text will explain in detail the positive electrode, the manufacturing method of the positive electrode, and the secondary battery.

[0042] positive electrode

[0043] In one aspect, the positive electrode includes: a current collector, a positive electrode mixture layer disposed on a portion of the current collector and comprising a positive electrode active material, and an insulating layer adjacent to the positive electrode mixture layer and disposed on a current collector where the positive electrode mixture layer is not disposed, wherein the positive electrode active material comprises a lithium metal phosphate compound, and the insulating layer comprises a non-aqueous binder containing a solution-polymerized conjugated diene copolymer and inorganic particles.

[0044] The positive electrode is characterized by containing lithium metal phosphate compounds in the positive electrode mixture layer and a solution-polymerized conjugated diene copolymer as a non-aqueous binder in the insulating layer.

[0045] Typically, when using non-aqueous adhesives, there is a problem of poor wet adhesion in the electrolyte-immersed state. Therefore, aqueous adhesives have been used, with emulsion-polymerized SBR being a representative example. Emulsion-polymerized SBR is classified as aqueous because it uses water as a solvent and polymerizes in the presence of emulsifiers and surfactants. When aqueous adhesives are used in the insulating layer coated at the end of the positive electrode, the positive electrode active material is extremely sensitive to moisture. Therefore, aqueous adhesives may affect battery performance in various ways and may cause problems such as gelation due to contact with the oil-based adhesives of the positive electrode slurry.

[0046] Therefore, using emulsion-polymerized SBR as an adhesive for the insulating layer requires a special process. The aforementioned problem can be solved by replacing the aqueous solvent of the emulsion-polymerized SBR with a non-aqueous organic solvent, thereby making its properties identical to the solvent composition of the cathode slurry.

[0047] However, replacing the aqueous solvent of the emulsion-polymerized SBR with a non-aqueous solvent requires additional pretreatment processes. Performing these pretreatments to supply the insulating layer, which is indispensable in the battery but constitutes a relatively small proportion of the battery, can lead to performance issues that are the main cause of a significant reduction in process efficiency and loss of cost competitiveness.

[0048] The above problems are solved by using a solution-polymerized conjugated diene copolymer as a binder for the insulating layer coated on the positive electrode.

[0049] The insulating layer may include an overlapping portion covering a portion of the positive electrode mixture layer at the part in contact with the positive electrode mixture layer.

[0050] As mentioned above, the overlapping part is the part that comes into contact with the positive electrode mixture layer, and it is the part where the most problems are concentrated when using oil-based adhesives and water-based adhesives, with frequent occurrences of problems such as easy peeling and cracking.

[0051] In the case of SBR with emulsion polymerization, there is no problem when the positive electrode active material of the positive electrode mixture layer is a lithium nickel oxide. However, when lithium metal phosphate compounds are used as the positive electrode active material, the surfactants inevitably present in the emulsion polymerization SBR due to the characteristics of the polymerization reaction can cause phenomena such as surface tension difference between the positive electrode slurry and the insulating composition, which may cause the mixture layer to lift or peel after drying. This can lead to problems such as damage to the insulating layer in the overlapping area or dents or cracks in part of the insulating layer.

[0052] In one aspect, the positive electrode contains a positive electrode active material containing a lithium metal phosphate compound in the positive electrode mixture layer, and the insulating layer used to insulate the mixture layer contains a solution-polymerized conjugated diene copolymer, thereby solving the aforementioned problems that occur at the overlap, and because it has excellent wet adhesion due to the absence of surfactants, peeling problems can be prevented even when immersed in electrolyte.

[0053] An insulating layer can be formed on the current collector and positive electrode mixture layer to a predetermined thickness. In this case, the thickness of the insulating layer can be from 10 μm to 30 μm, preferably from 15 μm to 25 μm, and more preferably from 17 μm to 23 μm. If the thickness of the insulating layer meets the above range, the adhesion of the insulating layer to the current collector and / or positive electrode mixture layer can be further improved.

[0054] The components of the positive electrode will be explained below.

[0055] (1) Adhesives containing solution-polymerized conjugated diene copolymers

[0056] In one aspect, the insulating layer is characterized by containing a solution-polymerized conjugated diene copolymer as an adhesive.

[0057] Solution-polymerized conjugated diene copolymers can be prepared by anionic living polymerization using diene monomers such as butadiene and aromatic vinyl monomers such as styrene in the presence of an initiator and an organic solvent. In this case, the contents of the diene monomers and aromatic vinyl monomers can range from 5% to 95% by weight, respectively. There are no particular restrictions on the specific polymerization conditions, polymerization additives, etc., of anionic living polymerization, as long as they do not violate common technical knowledge in the field.

[0058] The solution-polymerized conjugated diene copolymers exhibit a surfactant-free characteristic, meaning they are virtually surfactant-free. Here, "surfactant-free" means that surfactants are not detected at a detectable level, for example, less than 100 ppm, less than 50 ppm, or less than 30 ppm based on the total weight of the insulating layer. Due to this surfactant-free characteristic, unlike emulsion-polymerized SBRs, even when using lithium metal phosphate compounds as the positive electrode active material, problems that may occur in overlapping areas, such as layer peeling and insulating layer cracking, can be prevented, and adhesion in the electrolyte-immersed state can be excellent.

[0059] In addition to solution-polymerized conjugated diene copolymers, the adhesive may also contain polyvinylidene fluoride (PVDF). The presence of PVDF further enhances adhesion.

[0060] Based on 100 parts by weight of the insulating layer, the insulating layer may contain 5 to 60 parts by weight of adhesive, preferably 10 parts or more, 15 parts or more, 20 parts or more, or 25 parts or more, and less than 55 parts by weight, less than 50 parts by weight, less than 45 parts by weight, or less than 40 parts by weight. If the adhesive is included in the insulating layer within the above range, it can have a synergistic effect in preventing problems that occur in the overlap.

[0061] The adhesive may also include auxiliary adhesives, representative examples of which include aqueous or non-aqueous polymers comprising a single material or a mixture of two or more materials selected from the group consisting of: polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene, polyvinylpyrrolidone, polyacrylonitrile, polyvinylidene fluoride-trichloroethylene, polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE), polymethyl methacrylate, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, styrene-butadiene rubber (SBR), acrylonitrile-styrene-butadiene copolymer, and polyimide. Polyvinylidene fluoride (PVdF) is particularly preferred.

[0062] In this case, the weight ratio of the solution-polymerized conjugated diene copolymer to the auxiliary binder can be from 95:5 to 70:30, preferably from 90:10 to 75:25. If the above range is met, the above effects can be further optimized.

[0063] (2) Inorganic particles

[0064] In one aspect, the insulating layer is characterized by comprising a solution-polymerized conjugated diene copolymer as a binder, and also comprising inorganic particles.

[0065] The insulating layer serves to prevent high-risk events such as thermal runaway or explosion caused by short circuits between electrodes during abnormal battery operation; therefore, it inherently needs to possess the property of withstanding high temperatures without melting. Thus, an attempt was made to address this issue by incorporating heat-resistant inorganic particles into the insulating layer, which uses only conventional adhesives.

[0066] Therefore, the insulating layer in the positive electrode also contains inorganic particles, which, most importantly, enhance heat resistance. Since inorganic particles do not soften or melt even at high temperatures (e.g., above 900°C), including such inorganic particles in the insulating layer ensures that the electrode insulation remains intact even at extremely high temperatures.

[0067] The inorganic particles may include, for example, one or more selected from the group consisting of boehmite (AlOOH), aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), and zirconium oxide (ZrO2). Preferably, boehmite may be used, in which case excellent dispersibility is achieved while ensuring superior heat resistance, thus providing the advantage of uniform heat resistance throughout the insulation layer, and excellent adhesion retention even after electrolyte impregnation due to the presence of hydroxyl groups in the inorganic particles.

[0068] D of inorganic particles 50 The particle size can be from 0.1 μm to 5.0 μm, preferably from 0.1 μm to 3.0 μm, more preferably 0.3 μm or more or 0.5 μm or more, and is less than 2.0 μm or less or less than 1.5 μm. If the D of the inorganic particles... 50 If the above range is met, the agglomeration of inorganic particles in the insulating coating composition is minimized during the formation of the insulating layer, thereby forming an insulating layer with uniform thickness and surface.

[0069] Based on 100 parts by weight of the insulating layer, the insulating layer may contain 40 to 95 parts by weight of inorganic particles, preferably 45 parts by weight or more, 50 parts by weight or more, or 55 parts by weight or more, and less than 90 parts by weight, less than 85 parts by weight, less than 80 parts by weight, less than 75 parts by weight, or less than 70 parts by weight. If the content of inorganic particles meets the above ranges, the agglomeration of inorganic particles in the insulating coating composition is minimized during the formation of the insulating layer, thereby appropriately maintaining the viscosity of the composition and forming an insulating layer with uniform thickness and surface.

[0070] (3) Positive electrode mixture layer

[0071] In one aspect, the positive electrode is characterized by having a positive electrode mixture layer on the current collector. Furthermore, the positive electrode mixture layer comprises a lithium metal phosphate compound as the positive electrode active material, and may also comprise a conductive material and a binder.

[0072] There are no particular restrictions on the current collector, as long as it is conductive and does not cause chemical changes in the corresponding battery. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver can be used as the positive electrode current collector.

[0073] The thickness of the current collector can be from 3 μm to 100 μm, preferably from 8 μm to 80 μm, but is not limited thereto. In addition, fine irregularities can be formed on the surface of the current collector to improve the adhesion of the mixture film.

[0074] The positive electrode active material contains lithium metal phosphate compounds that can be represented by the following chemical formula 1.

[0075] [Chemical Formula 1]

[0076] Li 1+x [Fe 1-y M y ]PO4

[0077] In the above chemical formula 1, M includes one or more of the group consisting of Mn, Co, Ni, Al, Mg and Ti, and -0.5≤x≤0.5, 0≤y<1.

[0078] The lithium metal phosphate compound may be doped with M. In this case, the lattice structure and spacing in the olivine crystal structure, which is a crystal structure, are changed, thereby improving the diffusion of lithium ions. As a result, the electrochemical characteristics of the battery containing the positive electrode active material can be improved.

[0079] The x can be from -0.5 to 0.5, preferably above -0.3, above -0.1, or above 0, and can be below 0.5, below 0.4, below 0.3, below 0.2, or below 0.1.

[0080] The value of y can be greater than or equal to 0, and can be less than or equal to 1, and can be less than or equal to 0.90, 0.80, 0.70, 0.60, 0.50, 0.40, 0.30, 0.20, 0.10, or 0.05.

[0081] For example, the lithium metal phosphate compound may be, for example, LiFePO4.

[0082] The lithium metal phosphate compound of the present invention can be in the form of a single primary particle or in the form of irregular secondary particles consisting of 2 to 50 primary particles. Furthermore, the lithium metal phosphate compound may contain an olivine structure, specifically, it may be formed solely of an olivine structure. The coating of the present invention can be formed not only on secondary particles but also on primary particles. That is, the coating of the present invention can be uniformly present on the surface of primary particles existing within the secondary particles.

[0083] The coating may comprise a carbon coating with a graphite structure, and the coating thickness may be from 0.5 nm to 5 nm. If the coating thickness is within this range, it has the advantage of improving conductivity without interfering with the entry and exit of lithium ions. Specifically, the coating thickness may be 0.5 nm or more, 1.0 nm or more, 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, or 3.0 nm or more, and less than 5.0 nm.

[0084] The coating can be uniformly applied to the surface of a lithium metal phosphate compound. That is, the coating can be in thin film form. This coating can improve the ionic and electronic conductivity of a battery containing positive electrode active materials during charging and discharging. In addition to carbon, the coating may contain trace amounts of impurities such as nitrogen, oxygen, and hydrogen.

[0085] Based on the total weight of lithium metal phosphate compounds, the coating content can be from 0.5% to 3% by weight, thereby improving conductivity without interfering with the entry and exit of lithium ions.

[0086] Based on the total weight of the positive electrode mixture layer, the content of the positive electrode active material can be from 80% to 99% by weight, preferably 85% or more by weight, 88% or more by weight, 90% or more by weight, 92% or more by weight, 93% or more by weight, or 95% or more by weight, and is less than 98.5% by weight, less than 98% by weight, or less than 97.5% by weight. Content within the above ranges is preferred in terms of improving the capacity and energy density of the electrode and in optimizing the function of the conductive material and binder as auxiliary materials.

[0087] Conductive materials are components used to further improve the conductivity of the positive electrode active material. There are no particular limitations on the conductive material, as long as it is conductive and does not cause chemical changes in the battery. Examples include: carbon powder, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermally cracked carbon black; graphite powder, such as natural graphite, artificial graphite, or graphite with a highly developed crystal structure; conductive fibers, such as carbon fibers or metal fibers; fluorocarbon powder; conductive powder, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide or potassium titanate; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives. Specifically, to uniformly mix and improve the conductivity of the conductive material, it may include one or more components selected from the group consisting of activated carbon, graphite, carbon black, and carbon nanotubes (CNTs).

[0088] Based on the total weight of the positive electrode mixture layer, the content of conductive material can be from 0.1 wt% to 10.0 wt%. Preferably, the content of conductive material can be 0.2 wt% or more, 0.3 wt% or more, 0.5 wt% or more, or 0.7 wt% or more, and less than 8.0 wt%, 6.0 wt% or less, or 5.0 wt% or less. A higher amount of conductive material is more conducive to the formation of conductive pathways, but may lead to a decrease in capacity due to a relative reduction in the amount of active material. Although the amount added is not easy to control due to dispersion issues, the effect of forming conductive pathways can be maximized by optimizing the dispersion within the above range. Therefore, using conductive material within the above range is preferred.

[0089] Adhesives are used to improve the bonding between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples may include: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers with hydrogen substituted by Li, Na, or Ca, or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0090] Based on the total weight of the positive electrode mixture layer, the binder content can be from 0.1% to 10.0% by weight. Preferably, the binder content can be 0.2% or more by weight, 0.3% or more by weight, 0.5% or more by weight, or 0.7% or more by weight, and is less than 8.0% by weight, less than 6.0% by weight, or less than 5.0% by weight.

[0091] Method for manufacturing positive electrode

[0092] In one aspect, a method for manufacturing a positive electrode includes: (S1a) coating a positive electrode slurry containing a positive electrode active material onto a portion of a current collector; (S1b) coating an insulating coating composition onto a portion of the current collector adjacent to the area coated with the positive electrode slurry and not coated with the positive electrode slurry; and (S2) drying the positive electrode slurry and the insulating coating composition coated on the current collector to form a positive electrode mixture layer and an insulating layer, wherein the positive electrode active material comprises a lithium metal phosphate compound, and the insulating coating composition comprises a binder containing a solution-polymerized conjugated diene copolymer, an organic solvent, and inorganic particles.

[0093] The above-mentioned step S1a can be performed according to the usual positive electrode manufacturing method. Specifically, a positive electrode slurry prepared by dissolving or dispersing the positive electrode active material, binder and conductive material in a solvent can be coated on the positive electrode current collector, dried and then rolled to manufacture the positive electrode.

[0094] The S1b step described above can also be performed according to conventional methods for preparing insulating layers. For example, an insulating coating composition can be prepared by mixing and dispersing inorganic particles and an adhesive in an organic solvent. Specifically, the particles are added to the organic solvent and mixed to mix the components of the composition. In this case, mixing can be performed using mixing equipment known in the art, such as a homogenizer, but is not limited thereto.

[0095] The composition after the above mixing process is dispersed by grinding. Grinding can be carried out using a ball mill, bead mill, or basket mill, more specifically, a bead mill. At the same time, the degree of dispersion of the composition can be controlled by adjusting grinding conditions such as the number of times the composition passes through the ball mill, bead mill, or basket mill (hereinafter referred to as "passes") and the rotor speed.

[0096] Steps S1a and S1b described above can be performed simultaneously, or sequentially before the drying process in step S2. Specifically, a coating machine with multiple nozzles can be used, allowing the positive electrode slurry and the insulating coating composition to be coated onto the current collector simultaneously. Furthermore, the positive electrode slurry coating equipment and the insulating coating composition coating equipment can be arranged sequentially along the travel direction of the conveyor belt, thereby designing a process in which the coating is performed before drying.

[0097] Step S2 is a drying process using commonly used process conditions in the art, for example, drying can be carried out at a temperature of 120°C to 170°C, preferably 130°C to 160°C. This temperature range is more stringent than typical drying processes. If lithium metal phosphate compounds are used as the positive electrode active material, the solid content in the slurry with the same viscosity level is lower than that in slurries using different positive electrode active materials, resulting in a higher solvent content to be removed. Therefore, the drying process must be carried out under slightly more stringent conditions. In this case, after the drying process, problems such as peeling, cracking, or denting of the positive electrode mixture layer or insulating layer may occur, especially at overlapping areas. However, if the insulating layer of the embodiment of the present invention is used, this problem can be prevented.

[0098] Meanwhile, according to embodiments of the present invention, the solid content of the positive electrode slurry can be 50% to 70% by weight, preferably 55% to 65% by weight, and the solid content of the insulating coating composition can be 10% to 40% by weight, preferably 10% to 35% by weight. If the solid content is controlled within the above range, the positive electrode slurry and the insulating coating composition do not need to be mixed, and the problem of the insulating coating composition penetrating into the interface between the positive electrode mixture layer and the current collector can be avoided.

[0099] (1) Organic solvents

[0100] In one aspect, the insulating coating composition may be a mixture of inorganic particles and a binder in the presence of an organic solvent, and the positive electrode slurry may be a mixture of a positive electrode active material, a conductive material, and a binder in the presence of an organic solvent, wherein the organic solvent of the insulating coating composition and the organic solvent of the positive electrode slurry may be the same as or different from each other, and their application is not particularly limited, as long as they are used as non-aqueous organic solvents.

[0101] The organic solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and any one or a mixture of two or more of these can be used. The amount of organic solvent used is sufficient as long as it can dissolve or disperse the constituent particles while taking into account the coating thickness of the positive electrode slurry and the insulating coating composition, as well as the preparation yield, and subsequently achieves a viscosity that exhibits excellent thickness uniformity.

[0102] (2) Dispersant

[0103] In one aspect, the insulating coating composition may also include a dispersant. This dispersant is used to improve the dispersibility of particles that are not dissolved in the components.

[0104] Dispersants may include cellulose compounds, and non-limiting examples may include carboxymethyl cellulose, carboxyethyl cellulose or derivatives thereof, such as cationic substituted compounds with ammonium ions or monovalent metal ions thereof.

[0105] Secondary batteries

[0106] In one aspect, the secondary battery includes a positive electrode, a negative electrode facing the positive electrode, and a separator sandwiched between the positive and negative electrodes, and may contain an electrolyte injected therein after being housed in a battery casing. Since the positive electrode is the same as described above, its detailed description will be omitted here; only the remaining components will be described in detail below.

[0107] The secondary battery may optionally also include a battery housing housing an electrode assembly containing a positive electrode, a negative electrode, and a separator, as well as a sealing component for sealing the battery housing.

[0108] In a secondary battery, the negative electrode includes a negative current collector and a layer of negative electrode mixture disposed on the negative current collector.

[0109] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, heat-treated carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, and aluminum-cadmium alloys can be used. Furthermore, the thickness of the negative electrode current collector can typically range from 3 μm to 500 μm, and similar to the positive electrode current collector, fine irregularities can be formed on its surface to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various forms, such as films, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0110] The negative electrode mixture layer may optionally include a binder and a conductive material together with the negative electrode active material.

[0111] As anode active materials, compounds capable of reversibly inserting and de-intercalating lithium can be used. Specific examples include: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fibers, or amorphous carbon; metal compounds that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and metal oxides capable of doping and de-doping lithium, such as SiO₂. β(0<β<2), SnO2, vanadium oxide, or lithium vanadium oxide; or composites containing metal compounds and carbonaceous materials, such as Si-C composites or Sn-C composites, or any one or a mixture of two or more of these. Additionally, lithium metal films can be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as carbon materials. Representative examples of low-crystallinity carbon include soft carbon and hard carbon, while representative examples of high-crystallinity carbon include irregular, planar, sheet-like, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microspheres, mesophase pitch, and high-temperature heat-treated carbon, such as coke derived from petroleum or coal tar pitch.

[0112] Based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be from 80% to 99% by weight.

[0113] Adhesives are components used to facilitate the bonding between conductive materials, active materials, and current collectors, and are typically added in amounts ranging from 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of adhesives may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber, and various copolymers thereof.

[0114] The conductive material is a component used to further improve the conductivity of the negative electrode active material, and its addition amount relative to the total weight of the negative electrode mixture layer can be less than 10% by weight, preferably less than 5% by weight. There are no particular limitations on the conductive material, as long as it is conductive without causing chemical changes in the battery. Examples include: graphite, such as natural or artificial graphite; carbon black, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; conductive fibers, such as carbon fibers and metal fibers; fluorinated carbon; metal powders such as aluminum powder and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides, such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0115] The negative electrode mixture layer can be prepared by coating a negative electrode slurry composition, which is prepared by dissolving the negative electrode active material and optionally a binder and conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto a separate support and then laminating a film peeled off from the support onto the negative electrode current collector.

[0116] In secondary batteries, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular restriction, as long as it is a separator commonly used in lithium secondary batteries. In particular, separators with low impedance to ion movement in the electrolyte and excellent electrolyte retention are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, or ethylene / methacrylate copolymer), or their stacked structures of two or more layers. Alternatively, conventional porous nonwoven fabrics can be used, such as nonwoven fabrics made from high-melting-point glass fibers or polyethylene terephthalate fibers. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can optionally be used in single-layer or multi-layer structures.

[0117] The electrolyte used in the secondary battery can be any organic liquid electrolyte, inorganic liquid electrolyte, solid polymer electrolyte, gel polymer electrolyte, solid inorganic electrolyte, or molten inorganic electrolyte that can be used in the manufacture of secondary batteries, but is not limited to these.

[0118] Electrolytes may contain organic solvents and lithium salts.

[0119] As an organic solvent, any organic solvent can be used without particular restriction, as long as it can serve as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following solvents can be used as organic solvents: ester solvents, such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, such as dibutyl ether or tetrahydrofuran; ketone solvents, such as cyclohexanone; aromatic solvents, such as benzene and fluorobenzene; carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, such as ethanol and isopropanol; nitriles, such as R-CN (wherein R is a linear, branched, or cyclic C2 to C20 hydrocarbon group, and may contain double-bonded aromatic rings or ether bonds); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane; or sulfolane. Among these solvents, carbonate solvents are preferred, and more preferably, mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity linear carbonate compounds (e.g., methyl ethyl carbonate, dimethyl carbonate or diethyl carbonate, etc.) that can improve the charge and discharge performance of the battery are preferred.

[0120] Any compound can be used as a lithium salt without particular limitation, as long as it is a compound capable of providing lithium ions for secondary batteries. Specifically, the anion of the lithium salt can be selected from F...- Cl - ,Br - I - NO3 - N(CN)2 - BF4 - CF3CF2SO3 - (CF3SO2)2N - (FSO2)2N - CF3CF2(CF3)2CO - (CF3SO2)2CH - (SF5)3C - (CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 - CH3CO2 - SCN - and (CF3CF2SO2)2N - At least one of the constituent groups can be used as a lithium salt, such as LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. Preferably, the lithium salt is used in a concentration range of 0.1 M to 2.0 M. If the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move efficiently.

[0121] To improve battery life characteristics, suppress battery capacity reduction, and increase battery discharge capacity, the electrolyte may also contain one or more additives, such as alkylene carbonate halogenated compounds (e.g., ethylene difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoryltriamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolides, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. In this case, the content of the additives relative to the total weight of the electrolyte can be from 0.1% by weight to 5% by weight.

[0122] In another embodiment, the secondary battery may be an all-solid-state battery, in which case a solid electrolyte layer can be sandwiched between the positive and negative electrodes instead of a separator. Any solid electrolyte commonly used in the art can be used as the solid electrolyte, and there are no particular limitations.

[0123] The present invention will be described in more detail below with reference to embodiments. However, the following embodiments are merely illustrative and are not intended to limit the scope of the invention.

[0124] Preparation of insulating coating composition

[0125] Preparation Example 1

[0126] 60 parts by weight of D 50 It has a diameter of 1.0 μm and a specific surface area of ​​approximately 5.0 m². 2 / g to 8.5 m 2 / g of boehmite (product name: BP10, manufacturer: KEATON) was mixed with 35 parts by weight of solution-polymerized SBR (a linear copolymer obtained by solution polymerization of 40 parts by weight of styrene and 60 parts by weight of butadiene, with a weight average molecular weight of 250,000) as a binder and 5 parts by weight of PVDF (product name: KF9700, manufacturer: KUREHA) in NMP non-aqueous organic solvent to prepare a 1 kg mixture, which was then mixed for 1 hour using a homogenizer (product name: Dispermat LC, manufacturer: VMA).

[0127] Next, a dispersion process was carried out using a bead mill (product name: LS-1, manufacturer: NETZSCH) at a rotor speed of 3300 RPM, a discharge rate of 540 g / min per pass, and 8 passes to prepare the insulating coating composition.

[0128] Preparation Example 2

[0129] The insulating coating composition was prepared in the same manner as in Preparation Example 1, except that 65 parts by weight of boehmite were added and PVDF was not added to the adhesive.

[0130] Preparation Example 3

[0131] Except for the addition of 65 parts by weight of boehmite and 30 parts by weight of solution-polymerized SBR in the binder, the insulating coating composition was prepared in the same manner as in Preparation Example 1.

[0132] Preparation Example 4

[0133] Except for the addition of 70 parts by weight of boehmite, 30 parts by weight of solution-polymerized SBR in the binder, and the absence of PVDF, the insulating coating composition was prepared in the same manner as in Preparation Example 1.

[0134] Comparative Preparation Example 1

[0135] 100 parts by weight of a dispersion of emulsion-polymerized SBR (hereinafter referred to as BM451B, a product of ZEON) dispersed in water at a weight ratio of 60:40 were mixed with 500 parts by weight of N-methyl-2-pyrrolidone (NMP) solvent and stirred. The stirred mixture was then heated at 100°C to 120°C for 2 hours to completely evaporate the water, thereby preparing an NMP-substituted emulsion-polymerized SBR adhesive. Then, using this NMP-substituted SBR adhesive instead of solution-polymerized SBR, an insulating coating composition was prepared in the same manner as in Preparation Example 1.

[0136] Comparative Preparation Example 2

[0137] Except for adding 35 parts by weight of PVDF to the adhesive to replace the solution-polymerized SBR, the insulating coating composition was prepared in the same manner as in Preparation Example 2.

[0138] The weight-average molecular weight of the adhesive polymer used is a value converted from that of standard polystyrene, measured by gel permeation chromatography (GPC) under the following conditions, with a calibration curve prepared using standard polystyrene from the Agilent system.

[0139] <Measurement Conditions>

[0140] Measuring device: Agilent GPC (Agulent 1,200 series)

[0141] Column: Two PL Mixed B connections

[0142] Column temperature: 40℃

[0143] Eluent: Tetrahydrofuran

[0144] Flow rate: 1.0 mL / min

[0145] Concentration: ~1 mg / mL (100 μL injection)

[0146] Manufacturing of the positive electrode

[0147] Examples 1 to 4

[0148] 96 parts by weight of LiFePO4 as the positive electrode active material, 2 parts by weight of PVdF as the binder, and 2 parts by weight of carbon black as the conductive material were weighed and mixed in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry. Furthermore, the positive electrode slurry and the insulating coating compositions prepared in Examples 1 to 4 were simultaneously coated onto the current collector using a double-slit die coater, wherein the loading of the positive electrode mixture layer was 20 mg / cm³. 2The average thickness of the insulating layer was 20 µm. Subsequently, each electrode sample was dried at an average temperature of 130 °C to fabricate the positive electrode.

[0149] Comparative Example 1

[0150] Except that the insulating coating composition of Comparative Preparation Example 1 was used as the insulating coating composition, the positive electrode was manufactured in the same manner as in Example 1.

[0151] Comparative Example 2

[0152] Except that the insulating coating composition of Comparative Preparation Example 2 was used as the insulating coating composition, the positive electrode was manufactured in the same manner as in Example 1.

[0153] [Table 1]

[0154] Experiment Example 1: Appearance Evaluation

[0155] The surface portions of the insulating layers of the positive electrodes of Examples 1 to 4 and Comparative Examples 1 and 2 were photographed to confirm the presence of cracks or dents. Cross-sectional photographs of the positive electrodes were used to confirm the presence of peeling / lifting of the positive electrode mixture layer. Each positive electrode was immersed in an electrolyte (organic solvent EC:DMC=55:45, 1 M LiPF6) and then stored in an oven at 60°C for one week to confirm whether the insulating layer had peeled off. Photographs of the surface and cross-section of the insulating layers of the positive electrodes of Examples 1 and Comparative Example 1 were used as... Figures 1 to 4 attach.

[0156] [Table 2]

[0157] First, refer to photographs of the insulating layer surfaces of Example 1 and Comparative Example 1, respectively. Figure 1 and Figure 2 As shown in the figure, W I W indicates the insulation width. O Indicates the overlap width. (and) Figure 1 The difference lies in Figure 2 In the diagram, it can be confirmed that part B is concave, and that cracks, similar to those in part A, are present. Furthermore, refer to... Figure 3 and Figure 4 In the cross-section showing Example 1 Figure 3 The photographs confirmed that the positive electrode mixture layer and the insulating layer were well bonded to the current collector, but... Figure 4 In the cross-section of the positive electrode of Comparative Example 1, a portion of the positive electrode mixture layer peels off from the current collector and lifts up.

[0158] Furthermore, referring to Table 1 above, it was confirmed that in Examples 2 to 4, as in Example 1, no warping, peeling, or cracking occurred on the surface or cross-section. Additionally, in Comparative Example 2, it was confirmed that peeling occurred after wetting with the electrolyte because the PVDF adhesive used has the characteristic of being easily wetted by the electrolyte.

Claims

1. A positive electrode comprising: A current collector; a positive electrode mixture layer disposed on a portion of the current collector and comprising a positive electrode active material; and an insulating layer adjacent to the positive electrode mixture layer and disposed on a current collector where the positive electrode mixture layer is not disposed. wherein The insulating layer comprises an adhesive containing a solution-polymerized conjugated diene copolymer and inorganic particles.

2. The positive electrode according to claim 1, wherein The solution-polymerized conjugated diene copolymer comprises 5% to 95% by weight diene monomer units and 5% to 95% by weight aromatic vinyl monomer units.

3. The positive electrode according to claim 1, wherein The adhesive does not contain surfactants.

4. The positive electrode according to claim 1, wherein The insulating layer includes an overlap that covers a portion of the positive electrode mixture layer at the portion in contact with it.

5. The positive electrode according to claim 1, wherein The inorganic particles comprise one or more of the group consisting of boehmite (AlOOH), aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), and zirconium oxide (ZrO2).

6. The positive electrode according to claim 1, wherein The positive electrode active material comprises a lithium metal phosphate compound, which is represented by the following chemical formula 1: [Chemical Formula 1] Li 1+x [Fe 1-y M y ]PO4 In the above chemical formula 1, M includes one or more of the group consisting of Mn, Co, Ni, Al, Mg and Ti, and -0.5≤x≤0.5, 0≤y<1.

7. The positive electrode according to claim 1, wherein Based on 100 parts by weight of the insulating layer, the insulating layer comprises 40 to 90 parts by weight of the inorganic particles and 10 to 60 parts by weight of the adhesive.

8. The positive electrode according to claim 1, wherein The adhesive also includes an auxiliary adhesive, which comprises polyvinylidene fluoride.

9. The positive electrode according to claim 8, wherein The weight ratio of the solution-polymerized conjugated diene copolymer to the auxiliary binder is 95:5 to 70:

30.

10. The positive electrode according to claim 1, wherein The positive electrode mixture layer also includes an adhesive and a conductive material.

11. A method for manufacturing a positive electrode, the method comprising the following steps: (S1a) A positive electrode slurry containing a positive electrode active material is coated onto a portion of the current collector; (S1b) Apply an insulating coating composition to the current collector in the region adjacent to the region coated with the positive electrode paste and in the region not coated with the positive electrode paste; as well as (S2) The positive electrode paste and the insulating coating composition coated on the current collector are dried to form a positive electrode mixture layer and an insulating layer. The insulating coating composition comprises an adhesive containing a solution-polymerized conjugated diene copolymer, an organic solvent, and inorganic particles.

12. The method of claim 11, wherein, Steps S1a and S1b are performed before step S2, and simultaneously or sequentially.

13. The method of claim 11, wherein: The solids content of the positive electrode slurry is 50% to 70% by weight; and The solid content of the insulating coating composition is from 10% to 40% by weight.

14. A secondary battery comprising the positive electrode as described in claim 1.

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