Positive plate and preparation method thereof, battery and electric equipment

Abstract

The invention discloses a positive plate and a preparation method thereof, a battery and electric equipment. The positive plate comprises a current collector; the positive electrode active material layer is arranged on the surface of the current collector; the bonding layer is arranged on at least part of the circumferential edge of the surface of the current collector; wherein the bonding layer comprises an organic polymer, and the organic polymer comprises polyolefin resin and an acrylate copolymer. According to the positive plate disclosed by the invention, the bonding layer comprises the polyolefin resin and the organic polymer of the acrylate copolymer, so that the bonding force of the bonding layer to the current collector and the diaphragm is kept, and the short circuit in the battery caused by direct contact between the positive electrode and the negative electrode due to diaphragm shrinkage when the battery is in a high-temperature state is relieved. Therefore, the electrical property stability of the positive electrode is improved, the use stability of the positive plate is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode sheet and a preparation method thereof, a battery and an electrical device. Background Art

[0002] In the prior art, the coating commonly used on the edges of battery positive electrode tabs is an oily coating. The coating's slurry easily blends with the positive electrode dressing layer, resulting in an unclear boundary between the coating and the positive electrode dressing layer. Furthermore, the positive electrode dressing layer adjacent to the coating is not tightly bonded to the current collector and is prone to falling off. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the first object of the present invention is to provide a positive electrode sheet that maintains the adhesion of the adhesive layer to the current collector and separator, thereby mitigating the risk of direct contact between the positive and negative electrodes, which can result from separator shrinkage at high temperatures and cause internal short circuits in the battery.

[0004] The second object of the present invention is to provide a method for preparing a positive electrode sheet.

[0005] The third object of the present invention is to provide a battery.

[0006] A fourth object of the present invention is to provide an electrical device.

[0007] According to the first aspect of the present invention, the positive electrode sheet of the embodiment comprises a current collector; a positive electrode active material layer, wherein the positive electrode active material layer is disposed on the surface of the current collector; and an adhesive layer, wherein the adhesive layer is disposed on at least a portion of the circumferential edge of the surface of the current collector; wherein the adhesive layer comprises an organic polymer, and the organic polymer comprises a polyolefin resin and an acrylate copolymer.

[0008] In the positive electrode sheet according to an embodiment of the present invention, the adhesive layer comprises an organic polymer of a polyolefin resin and an acrylate copolymer. This maintains the adhesive layer's adhesion to the current collector and separator, mitigating the risk of internal short circuits in the battery caused by direct contact between the positive and negative electrodes due to separator shrinkage at high temperatures. This improves the electrical stability of the positive electrode and the operational stability of the positive electrode sheet, thereby extending the battery's service life.

[0009] According to some embodiments of the present invention, the organic polymer comprises, by mass percentage, 50% to 80% of a polyolefin resin and 20% to 50% of an acrylic ester copolymer.

[0010] According to some embodiments of the present invention, the organic polymer has a network structure with a cross-linked structure.

[0011] According to some embodiments of the present invention, the softening point of the acrylic ester copolymer is T, and T satisfies: 40°C≤T≤100°C.

[0012] According to some embodiments of the present invention, the polyolefin resin has a melting point of 50°C to 95°C.

[0013] According to some embodiments of the present invention, the polyolefin resin includes at least one of low-density polyethylene, polyethylene acrylic acid copolymer, polyethylene vinyl acetate copolymer, carboxyl-modified vinyl chloride vinyl acetate maleic anhydride, and styrene diene copolymer.

[0014] According to some embodiments of the present invention, the monomers of the acrylic ester copolymer include: multi-acrylic acid monomers, wherein the multi-acrylic acid monomers include: at least two of: soft acrylic acid monomers, hard acrylic acid monomers and functional acrylic acid monomers.

[0015] According to some embodiments of the present invention, the multi-acrylic monomer includes a soft acrylate monomer, a hard acrylate monomer and a functional acrylate monomer, and the multi-acrylic monomer includes: 50% to 70% of a soft acrylate monomer, 20% to 35% of a hard acrylate monomer and 2% to 20% of a functional acrylate monomer.

[0016] According to some embodiments of the present invention, the soft acrylic acid ester monomer includes: butyl acrylate, isooctyl acrylate, ethyl acrylate, lauryl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, isooctadecyl acrylate, nonadecyl acrylate, 2-methylnonadecyl acrylate, eicosyl acrylate, heneicosyl acrylate, docosyl acrylate, oleyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, At least one of 2-butyloctyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, heneicosyl methacrylate, docosyl methacrylate, halogenated compounds of the above organic substances and nitro-substituted compounds of the above organic substances; and / or the hard acrylate monomer includes: at least one of styrene, methyl methacrylate and acrylonitrile; and / or the functional acrylate monomer includes: at least one of 2-hydroxyethyl acrylate, glycidyl methacrylate and methacrylic acid.

[0017] According to some embodiments of the present invention, the bonding layer further comprises a ceramic material, and the ceramic material comprises at least one of boehmite, aluminum oxide, and magnesium oxide.

[0018] According to some embodiments of the present invention, the particle size range of the boehmite is: D10: 0.3 μm to 1 μm, D50: 0.6 μm to 3 μm, D99: 2 μm to 5 μm; and / or the specific surface area of the boehmite is: 2.5 m 2 / g~5.5m 2 / g; and / or the pH value of the boehmite is: 6 to 10; and / or the tap density of the boehmite is: 0.6 g / cm³ to 0.8 g / cm³.

[0019] According to some embodiments of the present invention, the thickness of the adhesive layer is d, and d satisfies: 20 μm≤d≤90 μm.

[0020] According to some embodiments of the present invention, the current collector is a metal foil or a composite foil.

[0021] According to some embodiments of the present invention, the positive electrode active material layer includes at least one of a lithium-containing positive electrode active material, a sodium-containing positive electrode active material, and a potassium-containing positive electrode active material.

[0022] The method for preparing a positive electrode sheet according to the second embodiment of the present invention comprises the following steps: disposing a positive electrode active material layer slurry on the surface of a current collector to form a positive electrode active material layer; An adhesive layer slurry is provided on at least a portion of a circumferential edge of the surface of the current collector to form an adhesive layer.

[0023] According to some embodiments of the present invention, the preparation of the bonding layer slurry includes the following steps: At 60° C. to 120° C., in a protective gas atmosphere, a solvent, a monomer of an acrylate copolymer, and an initiator are added to carry out a polymerization reaction to form an acrylate copolymer; Then, polyolefin resin is added and heated at 100° C. to 130° C. until the polyolefin resin is dissolved to obtain a glue solution, which is the adhesive layer slurry.

[0024] According to some embodiments of the present invention, ceramic material is added to the glue solution at 25° C. to 35° C. and mixed to obtain the bonding layer slurry.

[0025] According to some embodiments of the present invention, the bonding layer slurry includes, by mass percentage, 35% to 55% of a solvent and 45% to 65% of a solid, and, by mass percentage, 100 parts of the solid include 75 to 85 parts of the ceramic material and 15 to 25 parts of the organic polymer.

[0026] According to some embodiments of the present invention, the solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, toluene and xylene.

[0027] According to some embodiments of the present invention, at a temperature of 20°C to 25°C, the viscosity of the adhesive layer slurry is 15,000 Pa.s to 95,000 mPa.s at 1 inverse second and 1,500 Pa.s to 4,500 mPa.s at 50 inverse seconds.

[0028] According to some embodiments of the present invention, the ratio of the mass of the initiator to the mass of the monomer of the acrylate copolymer is: 0.2% to 2%; and / or the initiator includes: at least one of: an azo initiator, an organic peroxide initiator and an inorganic peroxide initiator.

[0029] According to some embodiments of the present invention, a cross-linking agent is added to the glue solution at 25° C. to 35° C. and mixed.

[0030] According to some embodiments of the present invention, the cross-linking agent includes at least one of melamine, methylated melamine, methylimine melamine and n-butylated melamine.

[0031] A battery according to an embodiment of the third aspect of the present invention includes: a positive electrode sheet, which is the positive electrode sheet according to the embodiment of the first aspect of the present invention, or the positive electrode sheet prepared by the preparation method of the embodiment of the second aspect of the present invention.

[0032] An electrical device according to an embodiment of a fourth aspect of the present invention comprises at least one battery according to an embodiment of the third aspect of the present invention.

[0033] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0034] The following is a positive electrode sheet according to an embodiment of the first aspect of the present invention.

[0035] According to an embodiment of the first aspect of the present invention, a positive electrode sheet comprises: a current collector, a positive electrode active material layer, and an adhesive layer. The positive electrode active material layer is disposed on the surface of the current collector. The positive electrode active material layer may be disposed only on one surface of the current collector in the thickness direction, or may be disposed on both sides of the current collector in the thickness direction. This is not specifically limited herein. The positive electrode active material layer is configured to undergo intercalation and deintercalation reactions with ions during the charging and discharging processes, thereby enabling the storage and release of electrical energy.

[0036] The adhesive layer is provided on at least a portion of the circumferential edge of the current collector surface. For example, the positive electrode active material layer is provided in the middle of the current collector surface, and the adhesive layer overlaps the edge of the positive electrode active material layer, thereby achieving the provision of the adhesive layer on the circumferential edge of the current collector surface. Preferably, at least a portion of the adhesive layer is provided at the tab, wherein, during the battery assembly process, the tab will be welded or bonded to the current collector to form a complete current transmission path. This is not specifically limited here.

[0037] This arrangement, on the one hand, prevents burrs on the edge of the current collector from penetrating the separator, causing internal short circuits in the battery and thermal runaway. On the other hand, the edge of the positive electrode sheet forms the adhesive layer. When the separator shrinks, the edge of the negative electrode sheet directly contacts the adhesive layer, avoiding direct contact with the positive electrode active material layer. Therefore, the adhesive layer mitigates the risk of direct contact between the positive and negative electrodes, which could cause internal short circuits in the battery due to separator shrinkage at high temperatures. This improves the electrical stability of the positive electrode and the operational stability of the positive electrode sheet, thereby extending the battery's service life.

[0038] The adhesive layer comprises an organic polymer. This facilitates adhesion of the adhesive layer to the current collector (e.g., a current collector). Furthermore, the organic polymer softens or melts under heat and pressure, penetrating the pores of the separator. Furthermore, it exhibits good affinity with the separator, ensuring initial adhesion between the adhesive layer and the current collector and separator. The majority of organic polymers are non-polar segments, which have a significant polarity difference from the electrolyte, resulting in low swelling. Consequently, even after immersion in the electrolyte, the organic polymer maintains the adhesive layer's strength, preventing it from falling off.

[0039] An adhesive layer is applied to the positive electrode sheet. Pressure and heat are applied to the adhesive layer, causing the thermoplastic polyolefin resin in the adhesive layer to melt and bond to the separator. After cooling, the positive electrode sheet and separator are bonded and fixed together. This prevents the separator from shrinking and causing contact between the positive and negative electrodes, leading to a short circuit, even when the battery cell is exposed to high temperatures. Furthermore, the separator can be directly hot-pressed, eliminating the need for applying hot-melt adhesive, effectively reducing the material and production costs of the battery. The separator can be a composite material of PP (polypropylene) and PE (polyethylene), but is not limited to this.

[0040] Specifically, organic polymers include polyolefin resins and acrylate copolymers. Among them, polyolefin resins are a type of thermoplastic polymer material formed by the polymerization of olefin monomers, which has good flexibility, chemical resistance, electrical insulation and processability. Polyolefin resins have good affinity with the diaphragm, and after being heated and softened, they can penetrate into the gaps between the pores of the diaphragm to achieve diaphragm bonding. Therefore, by adopting polyolefin resins, it is beneficial to improve the softness of the adhesive layer, avoid cracking of the adhesive layer, and extend the service life of the adhesive layer. Acrylate copolymers contain ester groups and other polar functional groups, and have a good bonding effect on current collectors (such as aluminum foil). Acrylate copolymers have excellent color durability, UV stability and chemical inertness. Therefore, the use of acrylate copolymers is beneficial to improving the durability of the adhesive layer, thereby improving the stability of the adhesive layer.

[0041] In the positive electrode sheet according to an embodiment of the present invention, the adhesive layer comprises an organic polymer of a polyolefin resin and an acrylate copolymer. This maintains the adhesive layer's adhesion to the current collector and separator, mitigating the risk of internal short circuits in the battery caused by direct contact between the positive and negative electrodes due to separator shrinkage at high temperatures. This improves the electrical stability of the positive electrode and the operational stability of the positive electrode sheet, thereby extending the battery's service life.

[0042] According to some embodiments of the present invention, the organic polymer comprises, by weight, 50% to 80% polyolefin resin and 20% to 50% acrylate copolymer. The reasonable content of polyolefin resin and acrylate copolymer in the organic polymer facilitates fully utilizing the functions of the polyolefin resin and acrylate copolymer, improving the softness of the adhesive layer, preventing cracking of the adhesive layer, and enhancing the durability of the adhesive layer, thereby improving the stability of the adhesive layer and extending its service life.

[0043] According to other embodiments of the present invention, the organic polymer has a network structure with a cross-linked structure. Cross-linking refers to the process of connecting linear polymer chains through chemical bonds to form a three-dimensional network structure. The network structure of the organic polymer refers to the reaction of hydroxyl or carboxyl groups between the polymer chains of the polyolefin resin and the acrylate copolymer to form a network structure, which helps to increase the mechanical strength of the adhesive layer, making the adhesive layer more durable. It can also improve the heat resistance of the adhesive layer and reduce the possibility of softening or melting at high temperatures.

[0044] According to some embodiments of the present invention, the softening point of the acrylic ester copolymer is T, where T satisfies the following: 40°C ≤ T ≤ 100°C. The softening point of an organic polymer is used to determine the temperature at which the organic polymer begins to soften or flow under heating conditions. The softening point of an organic polymer is typically measured using differential scanning calorimetry, dynamic mechanical analysis, melt index analysis, ring and ball analysis, or thermogravimetric analysis.

[0045] Softening point test method: Using a TMA (Thermal Mechanical Analysis) device, in an Ar atmosphere, raise the temperature from -30°C to 120°C at a rate of 5°C / min, using penetration mode, a 1.1mm flat probe, and a pressure of 0.5N. (The sample is prepared by pouring an acrylic copolymer liquid into a mold and baking it at 130°C for approximately 10 hours to obtain a film with a thickness of approximately 200 microns.) The temperature at which a sudden change in penetration thickness occurs is the softening point.

[0046] By setting the softening point of the acrylate copolymer to 40°C ≤ T ≤ 100°C, the melting temperature requirement of the adhesive layer is reduced, ensuring the adhesion of the adhesive layer to the diaphragm and the current collector under hot pressing conditions, which is conducive to the adhesion of the adhesive layer to the diaphragm and the current collector, thereby reducing the difficulty of preparing the positive electrode sheet and reducing costs.

[0047] According to some specific embodiments of the present invention, the melting point of the polyolefin resin is between 50°C and 95°C. The melting point refers to the temperature at which the polyolefin resin transitions from a solid to a liquid state under standard atmospheric pressure. At this temperature, the solid and liquid states of the polyolefin resin are in phase equilibrium. Therefore, controlling the melting point of the adhesive layer is more rational, reduces the processing difficulty of the adhesive layer, and improves the efficiency of the adhesive layer preparation.

[0048] The polyolefin resin includes at least one of low-density polyethylene, polyethylene acrylic acid copolymer, polyethylene vinyl acetate copolymer, carboxyl-modified vinyl chloride vinyl acetate maleic anhydride, and styrene diene copolymer. Low-density polyethylene is polyethylene with a high degree of branching, low crystallinity, and a low melting point. These polymers exhibit excellent processing and molding properties, as well as good adhesion, toughness, and wear resistance. Therefore, using at least one of these polymers as the polyethylene acrylic acid copolymer improves the adhesion between the adhesive layer and the separator, enhancing the usability of the adhesive layer.

[0049] According to some specific embodiments of the present invention, the original monomers of the acrylate copolymer include: a multi-component acrylic acid monomer, wherein the multi-component acrylic acid monomer includes at least two of a soft acrylate monomer, a hard acrylate monomer, and a functional acrylate monomer. The acrylate copolymer formed by polymerizing at least two of the multi-component acrylic acid monomers provides diversity, thereby improving the overall performance of the adhesive layer, fully utilizing the functions of the multiple acrylate copolymers, and thus enhancing the usability of the adhesive layer.

[0050] Polyacrylic acid monomers include soft acrylic acid ester monomers, hard acrylic acid ester monomers, and functional acrylic acid ester monomers. Polyacrylic acid monomers include 50% to 70% soft acrylic acid ester monomers, 20% to 35% hard acrylic acid ester monomers, and 2% to 20% functional acrylic acid ester monomers. The polymerization of soft acrylic acid ester monomers, hard acrylic acid ester monomers, and functional acrylic acid ester monomers produces a wide variety of acrylic acid copolymers, which improves the affinity between the adhesive layer slurry and the separator, and enhances the adhesion of the adhesive layer to the separator.

[0051] Among them, the soft acrylate monomers include: butyl acrylate, isooctyl acrylate, ethyl acrylate, lauryl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, isooctadecyl acrylate, nonadecyl acrylate, 2-methylnonadecyl acrylate, eicosyl acrylate, heneicosyl acrylate, docosyl acrylate, oleyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, 2-butyl methacrylate, At least one of octyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, heneicosyl methacrylate, docosyl methacrylate, the halogenated monomers of the above organic substances and the nitro-substituted monomers of the above organic substances; and / or the hard acrylate monomer includes: at least one of styrene, methyl methacrylate and acrylonitrile; and / or the functional acrylate monomer includes: at least one of 2-hydroxyethyl acrylate, glycidyl methacrylate and methacrylic acid.

[0052] The aforementioned soft acrylate monomers all have relatively long chain lengths, which helps improve the affinity between the adhesive layer and the separator, thereby enhancing the bonding strength between the adhesive layer and the separator. Hard acrylate monomers help increase the bulk strength of the organic polymer, thereby improving the electrolyte resistance of the adhesive layer. Functional acrylate monomers help improve the bonding strength between the adhesive layer and the current collector, and enhance the retention of bonding strength after electrolyte immersion.

[0053] According to some embodiments of the present invention, the bonding layer includes a ceramic material, and the ceramic material includes at least one of boehmite, aluminum oxide, and magnesium oxide. Boehmite, aluminum oxide, and magnesium oxide are all ceramic materials, which are beneficial to ensuring the insulating properties of the bonding layer. The organic polymer can bond the above-mentioned ceramic material particles and bond the above-mentioned ceramic material particles to the current collector (such as aluminum foil). As a result, the bonding layer achieves its insulating properties through the combined action of the above-mentioned ceramic material and the organic polymer. Specifically, when the above-mentioned ceramic material is added to the organic polymer, the above-mentioned ceramic material can help improve the dielectric properties and insulation strength of the bonding layer. This is because the presence of the above-mentioned ceramic material can increase the path length inside the bonding layer, making it difficult for current to pass through, thereby increasing the resistivity of the bonding layer.

[0054] Boehmite improves the adhesive layer's plasticity, wear resistance, and flame retardancy, as well as its mechanical strength, thermal stability, and corrosion resistance. Specifically, a boehmite-containing adhesive layer applied to the edges of the positive electrode active material layer forms a protective layer, preventing side reactions such as dendrite growth caused by direct contact between the positive electrode active material and the electrolyte during charge and discharge cycles. This reduces the risk of internal short circuits in the battery and improves battery safety. Furthermore, boehmite exhibits excellent heat absorption and thermal stability. When the current collector is coated with a boehmite-containing adhesive layer, it absorbs heat when the battery overheats, slowing the temperature rise and improving the battery's thermal stability. At high temperatures, boehmite maintains structural stability, reducing the risk of thermal runaway. Furthermore, boehmite mitigates the volume change of the positive electrode active material during charge and discharge, stabilizes the electrode / electrolyte interface, and reduces active material shedding, thereby extending the battery's cycle life. Alumina is a high-melting-point ceramic material with excellent electrical insulation properties, the ability to withstand high temperatures, and high mechanical strength. Magnesium oxide is also a material with excellent electrical insulation properties and has a very high melting point. Therefore, using at least one of boehmite, aluminum oxide, and magnesium oxide as the insulating material is beneficial for improving the insulation performance and mechanical strength of the adhesive layer.

[0055] According to some specific embodiments of the present invention, the boehmite particle size ranges are: D10: 0.3 μm to 1 μm, D50: 0.6 μm to 3 μm, and D99: 2 μm to 5 μm (the boehmite particle size is determined by volume distribution percentage). The boehmite particle size is analyzed by laser diffraction according to GB / T 19077-2016.

[0056] The specific surface area of boehmite is: 2.5m 2 / g~5.5m 2 / g. The specific surface area of boehmite refers to the total surface area per unit mass of boehmite. The specific surface area of boehmite is determined according to the national standard GB / T 19587-2017, Determination of the Specific Surface Area of Solids by the BET Method for Gas Adsorption.

[0057] The pH value of boehmite is 6-10. The pH value of boehmite is determined as follows: (1) Weigh a certain amount of boehmite powder and add an appropriate amount of deionized water or distilled water to form a uniform suspension; (2) Use a magnetic stirrer or ultrasonic oscillator to mix the suspension evenly to ensure that the boehmite particles are well dispersed in the water; (3) Insert a pH meter into the suspension to measure. For example, 3.50g of boehmite can be added to 100g of deionized water, stirred for 10 minutes, and the pH value can be measured.

[0058] The tap density of boehmite is 0.6g / cm³ to 0.8g / cm³. The tap density is measured by vibrating or tapping a boehmite powder sample to compact it. It is typically measured using a tap density meter.

[0059] Therefore, setting the particle size range of boehmite, the specific surface area of boehmite, the pH value of boehmite and the tap density of boehmite is beneficial to improving the interfacial free energy, porosity and specific surface area of boehmite, making the dispersibility and solubility of boehmite in the solvent good, so that the boehmite can fully play its role, thereby improving the thermal stability of the battery and increasing the cycle life of the battery.

[0060] The thickness of the adhesive layer is d, where d satisfies the following conditions: 20 μm ≤ d ≤ 90 μm. The thickness of the adhesive layer is the single-sided thickness, i.e., the thickness of the adhesive layer on one side of the thickness direction of the current collector. By setting the thickness of the adhesive layer to 20 μm ≤ d ≤ 90 μm, the thickness of the adhesive layer is more reasonable, ensuring the stability of the adhesive layer on the current collector and the separator, making the drying time of the adhesive layer more reasonable, and preventing the adhesive layer from falling off. At the same time, the adhesive layer is relatively soft, reducing the risk of cracking of the adhesive layer and improving the mechanical strength of the adhesive layer.

[0061] According to some specific embodiments of the present invention, the current collector is a metal foil or a composite foil. Metal foil has excellent electrical conductivity and mechanical strength, which helps support the positive electrode active material layer in the positive electrode sheet and helps maintain the stability of the current collector during repeated charging and discharging of the battery. Composite foils, such as current collectors with a three-layer "metal-polymer-metal" structure, combine the advantages of different materials, such as the conductivity of metals and the mechanical properties of polymers, to improve the energy density, cycle life, and safety of batteries.

[0062] According to some specific embodiments of the present invention, the current collector is aluminum foil. Aluminum foil has advantages such as light weight and high electrical conductivity, and aluminum foil is relatively low in cost. Therefore, using aluminum foil as the current collector is beneficial to the lightness and chemical stability of the current collector, while also helping to improve battery performance and control battery costs.

[0063] According to some specific embodiments of the present invention, the positive electrode active material includes: at least one of a lithium-containing positive electrode active material, a sodium-containing positive electrode active material and a potassium-containing positive electrode active material. The lithium-containing positive electrode active material has good ionic conductivity, moderate solvation ability and high electrochemical stability. The sodium-containing positive electrode active material has high solubility and good thermal stability, which can improve the ionic conductivity and charge and discharge efficiency of the positive electrode sheet. At the same time, the sodium-containing positive electrode active material has a low cost and less impact on the environment, which is beneficial to reducing the use cost and environmental performance of the positive electrode sheet. The potassium-containing positive electrode active material has high stability and can provide good ionic conductivity. Therefore, using at least one of the lithium-containing positive electrode active material, the sodium-containing positive electrode active material and the potassium-containing positive electrode active material as the positive electrode active material is beneficial to improving the ionic conductivity of the positive electrode sheet.

[0064] According to the method for preparing a positive electrode sheet of the second embodiment of the present invention, a positive electrode active material layer slurry is provided on the surface of the current collector to form a positive electrode active material layer, and an adhesive layer slurry is provided on at least part of the circumferential edge of the surface of the current collector to form an adhesive layer.

[0065] According to the method for preparing the positive electrode sheet of the embodiment of the present invention, the above-mentioned preparation method is relatively simple, which is conducive to improving the preparation efficiency of the positive electrode sheet, and is also conducive to improving the quality of the positive electrode sheet, thereby helping to improve the stability and reliability of the positive electrode sheet in the battery.

[0066] The preparation method of the bonding layer slurry comprises the following steps: At 60° C. to 120° C., in a protective gas atmosphere, a solvent, a monomer of an acrylate copolymer and an initiator are added to carry out a polymerization reaction to form an acrylate copolymer.

[0067] Then add polyolefin resin and mix at 100°C to 130°C. After the polyolefin resin is dissolved, a glue solution is obtained, which is the bonding layer slurry.

[0068] Conducting the reaction under a protective atmosphere helps isolate oxygen and moisture from the air, preventing oxidation or deliquescence of the reactants. This ensures the stability of the solvent, the monomers of the acrylate copolymer, and the initiator, thereby improving the stability of the polymerization reaction. Adding the polyolefin resin after the polymerization of the monomers of the acrylate copolymer prevents interference with the polymerization reaction of the acrylate copolymer, thereby facilitating the polymerization reaction. Adding the polyolefin resin to the post-polymerization solution forms a uniform and stable adhesive solution. This results in a relatively simple preparation method, which improves the efficiency of preparing the adhesive layer slurry and reduces its production cost.

[0069] For example, after the bonding layer slurry is applied to form a bonding layer, it is hot-pressed at about 80-100°C and a pressure of 0.2-0.8 MPa for 2-10 minutes. The bonding layer and the separator can stick together without falling off, thereby achieving the integration of the positive electrode sheet and the separator.

[0070] Furthermore, ceramic material is added to the adhesive solution at 25° C. to 35° C. and mixed to improve the uniformity of the adhesive layer slurry. This arrangement is conducive to improving the dielectric properties and insulation strength of the adhesive layer through the ceramic material.

[0071] Among them, in terms of mass percentage, the bonding layer slurry includes: 35% to 55% solvent and 45% to 65% solid. In terms of mass percentage, 100 parts of solid include 75 to 85 parts of ceramic material and 15 to 25 parts of organic polymer. Among them, 35% to 55% solvent is suitable for 45% to 65% solid, so that the solid is fully dispersed in the solvent to increase the mixing uniformity and stability of the bonding layer slurry, so as to facilitate the subsequent coating on the positive electrode. The content of solvent in the bonding layer slurry is relatively low, which is conducive to the drying of the bonding layer slurry and avoids the problem of unclear boundary caused by the mutual dissolution of the bonding layer slurry and the dressing layer. At the same time, it prevents the solvent in the slurry from migrating into the diaphragm during the drying process, thereby improving the bonding tightness between the diaphragm adjacent to the bonding layer and the current collector, and improving the bonding stability of the diaphragm on the current collector. The raw materials for the bonding layer slurry have low temperature requirements, making it easy to process the slurry into the bonding layer, which helps improve battery production efficiency and reduce battery production costs. The content of ceramic materials and organic polymers in the solid is relatively reasonable, fully meeting the bonding and insulation requirements of the bonding layer slurry, which helps improve the performance stability of the positive electrode sheet and extend its service life.

[0072] According to some specific embodiments of the present invention, the solvent includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, toluene, and xylene. These solvents have good solubility and can effectively dissolve polyolefin resins and acrylate copolymers, facilitating the formation of a uniform adhesive layer slurry and ensuring uniform coating of the adhesive layer slurry on the current collector, thereby improving the electrochemical performance and overall quality of the battery. For example, organic polymers are slightly soluble in N-methylpyrrolidone. However, during heating, the solubility of the organic polymer initially increases, causing the slurry viscosity to rapidly increase. Then, as the N-methylpyrrolidone rapidly evaporates, the slurry viscosity continues to increase, resulting in increasingly poor slurry fluidity until it becomes solid. As a result, the adhesive layer prevents cross-contamination with the positive electrode active material during baking, ultimately achieving overlapping coating.

[0073] According to some embodiments of the present invention, at a temperature of 20°C to 25°C, the viscosity of the adhesive layer slurry is 15000 Pa.s to 95000 mPa.s in 1 inverted second and 1500 Pa.s to 4500 mPa.s in 50 inverted seconds. This is conducive to maintaining the adhesion between the adhesive layer slurry and the current collector and the diaphragm, and preventing the generated adhesive layer from falling off. The viscosity of the adhesive layer slurry is tested using an advanced rotational rheometer (Anton Paar MCR302), and the viscosity is recorded at 0.01s -1 to the 2000s -1 The viscosity is 1s when discharging -1 , 50s -1 Viscosity assessment is used to determine the viscosity of the slurry.

[0074] Furthermore, the ratio of the mass of the initiator to the mass of the monomers of the acrylate copolymer is 0.2% to 2%. Setting the ratio of the initiator content to the monomer content of the acrylate copolymer to 0.2% to 2% helps ensure that the initiator initiates the polymerization of the acrylate copolymer, while avoiding initiator waste and reducing battery costs.

[0075] Initiators include at least one of an azo initiator, an organic peroxide initiator, and an inorganic peroxide initiator. These initiators can all decompose under heating to generate free radicals, which in turn trigger the formation of active free radicals in the monomer molecules of the organic polymer, initiating a chain polymerization reaction. In actual use, by selecting at least one of these initiators, the polymerization rate and molecular weight distribution of the organic polymer can be controlled to meet the requirements for preparing the adhesive layer slurry and improve the electrochemical performance of the battery.

[0076] According to some specific embodiments of the present invention, a cross-linking agent is added to the adhesive solution at 25°C to 35°C and mixed. The cross-linking agent is beneficial to promoting or controlling the formation of chemical bonds between the polymer chains of the polyolefin resin and the acrylate copolymer, thereby generating a cross-linked network structure, thereby improving the heat resistance, solvent resistance and wear resistance of the adhesive layer slurry. During the positive electrode baking process, the cross-linking agent will react with the hydroxyl or carboxyl groups on the polyolefin resin and the acrylate copolymer, causing the cross-linking agent to partially cross-link, forming a local network structure to obtain a certain cohesive strength, further improving the electrolyte resistance of the adhesive layer, maintaining the adhesion of the adhesive layer to the current collector and the separator, thereby improving the integration of the current collector, separator and positive electrode.

[0077] Furthermore, the crosslinking agent includes at least one of melamine, methylated melamine, methylimine melamine, and n-butylated melamine. These organic compounds are easily dispersed and mixed in the solvent, have high activity, and are suitable for rapidly completing the crosslinking process to form a stable network structure.

[0078] A battery according to an embodiment of the third aspect of the present invention includes: a positive electrode sheet, which is the positive electrode sheet according to the embodiment of the first aspect of the present invention, or a positive electrode sheet prepared by the preparation method according to the embodiment of the first aspect of the present invention; a separator; and a negative electrode sheet, wherein the positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, and the adhesive layer is in contact with the separator.

[0079] The battery according to the embodiment of the present invention is conducive to improving the charging and discharging stability of the battery, extending the service life of the battery, and improving the market competitiveness of the battery.

[0080] An electrical device according to an embodiment of a fourth aspect of the present invention comprises at least one battery according to an embodiment of the third aspect of the present invention.

[0081] The electric device according to the embodiment of the present invention is conducive to improving the operational stability of the electric device, enhancing the user experience, and improving the market competitiveness of the electric device.

[0082] The following embodiments of the present invention are described in detail. It should be noted that the following embodiments are illustrative and are intended only to explain the present invention and are not to be construed as limiting the present invention. In addition, unless otherwise expressly stated, all reagents used in the following embodiments are commercially available or can be synthesized according to methods described herein or known methods. Reaction conditions not listed are also readily available to those skilled in the art.

[0083] Example 1 Preparation of adhesive layer slurry: 500 parts of deionized water were added to a reactor. Isodecyl acrylate, styrene, 2-hydroxyethyl acrylate, and AIBN (2,2'-Azobisisobutyronitrile) were then added in a weight ratio of 60:35:5:0.5. The mixture was stirred at high speed for 2 hours at 80°C under a nitrogen atmosphere. After the reaction, the mixture was coagulated, washed, and dried to produce an acrylate copolymer. The acrylate copolymer had a softening point of 60°C.

[0084] Add NMP to the reactor, then add polyethylene acrylic acid copolymer with a melting point of 78°C, raise the temperature to 115°C, stir at high speed for 2 hours, and then cool to 80°C. The mass ratio of polyethylene acrylic acid copolymer to acrylate copolymer is 7:3. After it is fully dissolved and forms a uniform solution, slowly cool to room temperature to obtain a glue solution with a solid content of 25%.

[0085] Take 100 parts of the above glue solution, 0.075 parts of methyl ether melamine, then add 75 parts of boehmite and 25 parts of NMP, and stir at high speed for 2 hours to obtain a ceramic slurry with a solid content of 36%. The particle size of the boehmite is: D10: 0.5μm, D50: 2μm, D99: 4μm, and the specific surface area of the boehmite is 3.0m 2 / g, the pH value of boehmite is 7, and the tap density of boehmite is 0.6g / cm³.

[0086] Preparation of the positive electrode sheet: Weigh 1 kg of lithium iron phosphate (positive electrode active material), 10 g of carbon nanotubes (positive electrode conductive agent), and 20 g of PVDF (polyvinylidene fluoride) (positive electrode binder) into 1 kg of NMP solvent, and then stir in a blender for 120 minutes to form a stable and uniform slurry of the positive electrode active material layer.

[0087] The slurry of the positive electrode active material layer and the slurry of the adhesive layer are overlapped and evenly coated on the surface of the current collector (aluminum foil), and then placed in an oven and dried at 130°C to obtain the positive electrode active material layer and the adhesive layer, wherein the thickness of the adhesive layer is 20 μm.

[0088] Test the penetration width between the positive electrode active material layer and the bonding layer; Test the bonding strength between the adhesive layer and the current collector; Place a layer of PP or PE diaphragm on the surface of the adhesive layer, and then hot press it in a hot press at 100℃ and 0.5MPa for 10 minutes to test the adhesion between the diaphragm and the adhesive layer.

[0089] The electrodes with un-hot-pressed diaphragms and hot-pressed diaphragms were placed in the electrolyte respectively and soaked at 60°C for 7 days. After taking them out, observe whether the bonding layer and the current collector, as well as the bonding layer and the diaphragm are falling off. If they are not falling off, bake the electrodes in a 70-degree Celsius forced air drying oven for 1 hour, and then test the bonding strength between the bonding layer and the current collector, as well as the bonding layer and the diaphragm respectively.

[0090] Example 2 Example 2 is basically the same as Example 1, except that the polyethylene acrylic acid copolymer is replaced with polyethylene vinyl acetate copolymer, which has a melting point of 70°C.

[0091] Example 3 Example 3 is substantially the same as Example 1, except that the mass ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 5:5.

[0092] Example 4 Example 4 is substantially the same as Example 1, except that the mass ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 8:2.

[0093] Example 5 Example 5 is substantially the same as Example 1, except that the mass ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 4:6.

[0094] Example 6 Example 6 is substantially the same as Example 1, except that the weight ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 9:1.

[0095] Example 7 Example 7 is basically the same as Example 1, except that a glue solution with a solid content of 30% is prepared, 66.67 parts of the above glue solution, 0.075 parts of methyl ether melamine, 80 parts of boehmite, and 6.33 parts of NMP are added, and the mixture is dispersed and stirred at high speed for 2 hours to obtain a ceramic slurry with a solid content of 65%.

[0096] Example 8 Example 8 is basically the same as Example 1, except that a glue solution with a solid content of 15% is prepared, 100 parts of the above glue solution, 0.075 parts of methyl ether melamine, 85 parts of boehmite, and 37.31 parts of NMP are added, and the mixture is dispersed and stirred at high speed for 2 hours to obtain a ceramic slurry with a solid content of 45%.

[0097] Example 9 Example 9 is basically the same as Example 1, except that the particle sizes of boehmite are: D10: 0.3 μm, D50: 0.6 μm, D99: 2 μm, and the specific surface area of boehmite is 5.5 m 2 / g, the pH value of boehmite is 6, and the tap density of boehmite is 0.6g / cm³.

[0098] Example 10 Example 10 is basically the same as Example 1, except that the particle sizes of boehmite are: D10: 1 μm, D50: 3 μm, D99: 5 μm, and the specific surface area of boehmite is 2.5 m 2 / g, the pH value of boehmite is 10, and the tap density of boehmite is 0.8g / cm³.

[0099] Example 11 Example 11 is substantially the same as Example 1, except that the thickness of the adhesive layer is 50 μm.

[0100] Example 12 Example 12 is substantially the same as Example 1, except that the thickness of the adhesive layer is 90 μm.

[0101] Example 13 Example 13 is substantially the same as Example 1, except that no cross-linking agent is included.

[0102] Example 14 Example 14 is substantially the same as Example 1, except that boehmite is replaced with alumina.

[0103] Example 15 Example 15 is substantially the same as Example 1, except that boehmite is not included.

[0104] Example 16 Example 16 is substantially the same as Example 1, except that the softening point of the acrylate copolymer is 40°C.

[0105] Example 17 Example 17 is substantially the same as Example 1, except that the softening point of the acrylate copolymer is 100°C.

[0106] Comparative Example 1 Comparative Example 1 is substantially the same as Example 1, except that the weight ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 0:100.

[0107] Comparative Example 2 Comparative Example 2 is substantially the same as Example 1, except that the weight ratio of the polyethylene acrylic acid copolymer to the acrylic ester copolymer is 100:0.

[0108] Performance Testing 1. Penetration width: Magnify the overlapped coated positive electrode sheet 10-50 times under a microscope and observe the width of the two coating layers in the overlapped area. Penetration refers to a certain degree of mixing or contamination between the slurry of the positive electrode active material layer and the slurry of the bonding layer.

[0109] 2. Adhesion: Adopt 180° peel strength test method, tensile speed is 50mm / min; refer to GB / T2792.

[0110] Table 1 Test data of Examples 1 to 17 and Comparative Examples 1 to 2

[0111] Test result analysis Referring to Examples 1-17, it can be found that when the coating on the surface of the positive electrode active material includes both a ceramic material and an organic polymer, the bonding layer in the prepared positive electrode sheet has good adhesion to both the current collector and the separator, fully utilizing the bonding layer's function. By comparing Examples 1, 3, and 4 with Examples 5 and 6, it can be found that when the organic polymer includes 50% to 80% polyolefin resin and 20% to 50% acrylate copolymer, the bonding ability of the bonding layer to the current collector and the separator can be further guaranteed. As a result, when the battery cell is exposed to high temperature, the separator will not shrink and short-circuit due to contact between the positive and negative electrodes. At the same time, the separator can be directly hot-pressed without the need to coat it with hot-melt adhesive, effectively reducing the material cost and production cost of the battery.

[0112] Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "example," "specific example," or "some examples" means that a specific feature, structure, material, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0113] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A positive electrode sheet, characterized in that: include: current collector; a positive electrode active material layer, the positive electrode active material layer being provided on the surface of the current collector; an adhesive layer, the adhesive layer being provided on at least a portion of a circumferential edge of a surface of the current collector; Wherein, the adhesive layer comprises an organic polymer, The organic polymer includes polyolefin resin and acrylate copolymer.

2. The positive electrode sheet according to claim 1, characterized in that Calculated by mass percentage, the organic polymer includes: 50% to 80% of polyolefin resin and 20% to 50% of acrylic ester copolymer.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The organic polymer has a network structure with a cross-linked structure.

4. The positive electrode sheet according to claim 1 or 2, characterized in that: The softening point of the acrylic ester copolymer is T, and T satisfies: 40°C≤T≤100°C.

5. The positive electrode sheet according to claim 1 or 2, characterized in that: The melting point of the polyolefin resin is 50°C to 95°C.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The polyolefin resin includes at least one of low-density polyethylene, polyethylene acrylic acid copolymer, polyethylene vinyl acetate copolymer, carboxyl-modified vinyl chloride vinyl acetate maleic anhydride, and styrene diene copolymer.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The monomers of the acrylic ester copolymer include: multi-component acrylic acid monomers, wherein the multi-component acrylic acid monomers include: at least two of soft acrylic ester monomers, hard acrylic ester monomers and functional acrylic ester monomers.

8. The positive electrode sheet according to claim 7, characterized in that: The multi-acrylic monomers include soft acrylate monomers, hard acrylate monomers and functional acrylate monomers, and the multi-acrylic monomers include: 50% to 70% of soft acrylate monomers, 20% to 35% of hard acrylate monomers and 2% to 20% of functional acrylate monomers.

9. The positive electrode sheet according to claim 8, characterized in that: The soft acrylic ester monomers include: butyl acrylate, isooctyl acrylate, ethyl acrylate, lauryl acrylate, decyl acrylate, isodecyl acrylate, undecyl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, octadecyl acrylate, isooctadecyl acrylate, nonadecyl acrylate, 2-methylnonadecyl acrylate, eicosyl acrylate, heneicosyl acrylate, behenyl acrylate, oleyl methacrylate, decyl methacrylate, isodecyl methacrylate, undecyl methacrylate, dodecyl methacrylate, 2-butyloctyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, pentadecyl methacrylate, hexadecyl methacrylate, heptadecyl methacrylate, octadecyl methacrylate, nonadecyl methacrylate, eicosyl methacrylate, heneicosyl methacrylate, behenyl methacrylate, at least one of the halogenated compounds of the above organic substances and the nitro-substituted compounds of the above organic substances; and / or The hard acrylate monomer comprises: at least one of styrene, methyl methacrylate and acrylonitrile; and / or The functional acrylate monomer includes at least one of 2-hydroxyethyl acrylate, glycidyl methacrylate and methacrylic acid.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The bonding layer further includes a ceramic material, and the ceramic material includes at least one of boehmite, aluminum oxide, and magnesium oxide.

11. The positive electrode sheet according to claim 10, characterized in that: The boehmite has a particle size range of: D10: 0.3 μm to 1 μm, D50: 0.6 μm to 3 μm, D99: 2 μm to 5 μm; and / or The specific surface area of the boehmite is: 2.5m 2 / g~5.5m 2 / g; and / or The pH value of the boehmite is: 6 to 10; and / or The tap density of the boehmite is 0.6 g / cm³ to 0.8 g / cm³.

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that: The thickness of the adhesive layer is d, and d satisfies: 20 μm≤d≤90 μm.

13. The positive electrode sheet according to any one of claims 1 to 12, characterized in that: The positive electrode active material layer includes at least one of a lithium-containing positive electrode active material, a sodium-containing positive electrode active material, and a potassium-containing positive electrode active material.

14. A method for preparing a positive electrode sheet according to any one of claims 1 to 13, characterized in that: Disposing a positive electrode active material layer slurry on a surface of the current collector to form a positive electrode active material layer; An adhesive layer slurry is provided on at least a portion of a circumferential edge of the surface of the current collector to form an adhesive layer.

15. The preparation method according to claim 14, characterized in that The preparation of the bonding layer slurry comprises the following steps: At 60° C. to 120° C., in a protective gas atmosphere, a solvent, a monomer of an acrylate copolymer, and an initiator are added to carry out a polymerization reaction to form an acrylate copolymer; Then, polyolefin resin is added and heated at 100° C. to 130° C. until the polyolefin resin is dissolved to obtain a glue solution, which is the adhesive layer slurry.

16. The preparation method according to claim 15, characterized in that At 25° C. to 35° C., ceramic material is added to the glue solution and mixed to obtain the bonding layer slurry.

17. The preparation method according to claim 16, characterized in that In terms of mass percentage, the adhesive layer slurry comprises: 35% to 55% solvent and 45% to 65% solid. In terms of mass percentage, 100 parts of solids include 75 to 85 parts of the ceramic material and 15 to 25 parts of the organic polymer.

18. The preparation method according to claim 17, characterized in that: The solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, ethyl acetate, toluene and xylene.

19. The preparation method according to claim 17, characterized in that At a temperature of 20°C to 25°C, the viscosity of the adhesive layer slurry is 15,000 Pa.s to 95,000 mPa.s at 1 inverse second and 1,500 Pa.s to 4,500 mPa.s at 50 inverse seconds.

20. The preparation method according to claim 16, characterized in that The ratio of the mass of the initiator to the mass of the monomer of the acrylate copolymer is: 0.2% to 2%; and / or The initiator comprises at least one of an azo initiator, an organic peroxide initiator and an inorganic peroxide initiator.

21. The preparation method according to claim 15 or 16, characterized in that: Add a cross-linking agent to the glue solution at 25° C. to 35° C. and mix.

22. The preparation method according to claim 21, characterized in that The cross-linking agent comprises at least one of melamine, methyl ether melamine, methylimine melamine and n-butyl ether melamine.

23. A battery, characterized in that: include: A positive electrode sheet, wherein the positive electrode sheet is the positive electrode sheet according to any one of claims 1 to 13; or a positive electrode sheet prepared by the preparation method according to any one of claims 14 to 22.

24. An electrical device, characterized in that: Comprising at least one battery according to claim 23.

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