Diaphragm and application thereof

Abstract

The invention relates to a diaphragm and application thereof. The diaphragm comprises a sulfonated base membrane and a ceramic coating coated on at least one side of the sulfonated base membrane, and ceramic slurry for forming the diaphragm coating comprises the following components in percentage by mass: 15%-40% of aluminum oxide, 1.0%-3.0% of a binder, 0.2%-1.2% of an additive, 0.2%-1.2% of a dispersing agent, 0.02%-0.2% of an auxiliary agent and the balance of deionized water. According to the scheme provided by the invention, the puncture resistance of the diaphragm can be improved, and the zero electricity rate of the nickel-metal hydride battery is reduced.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to separators and their applications. Background Technology

[0002] Nickel-metal hydride (NiMH) batteries, with their high safety, high power characteristics, wide operating temperature range, and excellent cycle durability, have become a key energy solution in fields such as hybrid electric vehicles, special equipment, high-reliability consumer electronics, and backup power supplies. However, facing the rapid development of electrification, intelligentization, and extreme application scenarios, the market has an urgent need for continuous optimization of the energy density and self-discharge rate of NiMH batteries, driving the technology to evolve towards higher efficiency and wider adaptability.

[0003] To achieve higher capacity within limited design space, high-capacity nickel-metal hydride (NiMH) batteries are typically forced to use thinner separators. However, this significantly reduces the separator's puncture resistance, making it highly susceptible to punctures by electrode burrs or particles during battery winding or assembly. This can trigger micro-short circuits, causing the battery to fail with "zero voltage" during formation and capacity testing. This not only directly reduces production yield and increases manufacturing costs but also potentially increases the safety risks of NiMH batteries.

[0004] In conclusion, developing a novel separator with high puncture resistance is of great significance for achieving low zero-rate in high-capacity nickel-metal hydride batteries. Summary of the Invention

[0005] To address or partially address the problems existing in related technologies, this application provides a separator and its application, which has excellent puncture resistance and ultimately significantly reduces the zero-charge rate of nickel-metal hydride batteries.

[0006] The first aspect of this application provides a diaphragm, wherein the diaphragm comprises a sulfonated base membrane and a ceramic coating coated on at least one side of the sulfonated base membrane, wherein the ceramic slurry used to form the diaphragm coating comprises, by mass percentage, 15% to 40% alumina, 1.0% to 3.0% binder, 0.2% to 1.2% additives, 0.2% to 1.2% dispersant, 0.02% to 0.2% auxiliary agent, and the balance being deionized water.

[0007] The diaphragm as described in the first aspect, wherein the median particle size D50 of the alumina is 1.0 μm to 2.0 μm.

[0008] The diaphragm as described in the first aspect, wherein the binder comprises at least one selected from polyacrylol, cyanoacrylate, cyanoacrylate-polyethylene glycol, and polyvinyl acetate.

[0009] The diaphragm as described in the first aspect, wherein the additive comprises at least one of sodium carboxymethyl cellulose, polyethylene glycol, sodium polyacrylate, and polyethylene oxide.

[0010] The diaphragm as described in the first aspect, wherein the dispersant comprises at least one selected from sodium hexametaphosphate, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfonate; and / or, The additives include at least one of polyoxyethylene, polyoxypropylene, pentylenetetrazol ether, polyoxyethylene fatty alcohol ether, and alkyl naphthalene sulfonate.

[0011] As described in the first aspect, the sulfonated membrane comprises a sulfonated polypropylene membrane and / or a sulfonated polyethylene membrane; and / or, The degree of sulfonation of the sulfonated base film is 0.5%~0.7%.

[0012] As described in the first aspect, the diaphragm has a thickness of 0.08 mm to 0.10 mm; and / or, The thickness of the ceramic coating is 2.5μm to 4.5μm.

[0013] The diaphragm as described in the first aspect, wherein the ceramic slurry is prepared according to the following steps: According to the mass ratio, the alumina is mixed with deionized water, and the pH value is adjusted to 3.5~4.5 to obtain an alumina suspension with a solid content of 25%~35%. The alumina suspension is mixed with the binder, the additive, the dispersant, and the auxiliary agent to obtain the ceramic slurry.

[0014] The diaphragm as described in the first aspect, wherein the diaphragm is prepared according to the following steps: The ceramic slurry is coated onto at least one side of the sulfonated base membrane and then dried to obtain the diaphragm. The drying temperature of the drying process is 50℃~90℃, and the drying time is 10min~40min.

[0015] A second aspect of this application provides a battery, wherein the battery includes a separator as described in the first aspect.

[0016] The technical solution provided in this application can include the following beneficial effects: by precisely controlling the mass ratio of alumina, binder, additives, dispersants, and auxiliaries, and fully leveraging their synergistic effects, a coating "skeleton" with both excellent puncture resistance and high-temperature stability can be constructed on the diaphragm, while ensuring sufficient ion transport channels. This system effectively solves the problems of particle agglomeration and stability that easily occur in high-solids content slurries, thereby endowing the ceramic slurry with good coating processability and facilitating the formation of a uniform, defect-free ceramic coating. Furthermore, the high density of sulfonic acid groups on the surface of the sulfonated base film undergoes deep interfacial synergy with the functional components in the ceramic coating: the polar groups in the binder form a strong hydrogen bond network or acid-base ion crosslinking with the sulfonic acid groups; the additives act as "molecular bridges," condensing with the hydroxyl groups on the alumina surface at one end and chemically bonding with the sulfonic acid groups at the other end; and the mechanical interlocking formed by the coordination of Lewis acid sites on the alumina surface with the sulfonic acid groups and the excellent wetting and penetration of the ceramic slurry on the hydrophilic sulfonated surface significantly optimizes the interfacial adhesion between the ceramic coating and the sulfonated base film, and improves the stability under long-term electrochemical conditions. Ultimately, this can greatly enhance the puncture resistance of the separator and effectively reduce the zero-charge rate of nickel-metal hydride batteries during production and use.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0018] To facilitate understanding of this application, it will be described in detail below. However, before describing this application in detail, it should be understood that this application is not limited to the specific embodiments described. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be restrictive.

[0019] Where a numerical range is provided, it should be understood that every intermediate value between the upper and lower limits of the range and any other specified or intermediate value within the specified range is covered within this application. The upper and lower limits of these smaller ranges may be independently included in the smaller range and are also covered within this application, subject to any explicitly excluded limits within the specified range. Where the specified range includes one or two limits, the range excluding any or both of those included limits is also included within this application.

[0020] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. While the methods and materials described herein, or any equivalent methods and materials, may also be used in the implementation or testing of this application, preferred methods and materials are now described.

[0021] To achieve higher capacity within limited design space, high-capacity nickel-metal hydride (NiMH) batteries are typically forced to use thinner separators. However, this significantly reduces the separator's puncture resistance, making it highly susceptible to punctures by electrode burrs or particles during battery winding or assembly. This can trigger micro-short circuits, causing the battery to fail with "zero voltage" during formation and capacity testing. This not only directly reduces production yield and increases manufacturing costs but also potentially increases the safety risks of NiMH batteries.

[0022] To address the aforementioned issues, this application provides a diaphragm comprising a sulfonated base membrane and a ceramic coating applied to at least one side of the sulfonated base membrane. The ceramic slurry used to form the diaphragm coating comprises, by mass percentage, 15%–40% alumina, 1.0%–3.0% binder, 0.2%–1.2% additives, 0.2%–1.2% dispersant, 0.02%–0.2% auxiliary agents, with the balance being deionized water.

[0023] This application does not limit the specific parameters of alumina, which can be selected according to actual needs. Alumina has high hardness, excellent thermal stability and chemical stability, and can effectively resist the puncture of electrode burrs and impurity particles. It does not participate in the electrochemical reaction of the battery and is suitable for electrolyte systems of different types.

[0024] This application does not limit the specific choice of binder; it can be selected according to actual needs. For example, polyacryl alcohol, cyanoacrylate, cyanoacrylate-polyethylene glycol, polyvinyl formaldehyde, polyvinylidene fluoride, polyurethane, and polyvinyl alcohol can be selected. The binder of this application can bond the dispersed ceramic particles together to form a continuous porous coating film with sufficient cohesion, preventing the coating from pulverizing or shedding powder during drying, slitting, or winding, and ensuring that the ceramic coating can firmly adhere to the separator surface, preventing delamination or peeling during battery assembly or use. At the same time, it can give the ceramic coating high flexibility and bending performance, enabling it to withstand the mechanical stress during battery winding or stacking without cracking, and also ensuring sufficient wetting of the electrolyte and unobstructed ion channels.

[0025] This application does not limit the specific selection of additives; they can be selected according to actual needs. For example, sodium carboxymethyl cellulose, polyethylene glycol, sodium polyacrylate, polyethylene oxide, silane coupling agents, boron nitride, etc., can be selected. The additives in this application can play a role in thickening and dispersing, increasing the viscosity of the slurry, enhancing suspension stability and anti-settling properties.

[0026] This application does not limit the specific selection of the dispersant; it can be selected according to actual needs, such as sodium hexametaphosphate, hexadecyltrimethylammonium bromide, sodium dodecyl sulfonate, etc. The dispersant of this application can disperse agglomerated particles, ensuring that the particles remain suspended in the solvent for a long time, uniformly, and stably, forming a uniform and stable ceramic slurry.

[0027] This application does not limit the specific selection of additives; they can be selected according to actual needs. For example, polyoxyethylene, polyoxypropylene, pentanetetraethylene ether, polyoxyethylene fatty alcohol ether, alkyl naphthalene sulfonate, etc., can be selected. The additives in this application can play a role in wetting, defoaming, and leveling, reducing the surface tension of the slurry, improving the wetting and spreading ability of the ceramic slurry, reducing the stability of bubbles in the slurry, and improving the uniformity of the coating.

[0028] The ceramic slurry of this application contains 15% to 40% by mass of alumina, for example, the mass percentage of alumina can be 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0029] The mass percentage of binder in the ceramic slurry of this application is 1.0% to 3.0%, for example, the mass percentage of binder can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, etc.

[0030] The additives in the ceramic slurry of this application have a mass percentage content of 0.2% to 1.2%, for example, the mass percentage content of the additives can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, etc.

[0031] The mass percentage of dispersant in the ceramic slurry of this application is 0.2% to 1.2%, for example, the mass percentage of dispersant can be 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, etc.

[0032] The mass percentage of additives in the ceramic slurry of this application is 0.02% to 0.2%, for example, the mass percentage of additives can be 0.02%, 0.05%, 0.1%, 0.15%, 0.2%, etc.

[0033] According to the above-mentioned solution provided in this application, the separator exhibits excellent puncture resistance and can effectively reduce the zero-charge rate of the battery. The applicant analyzed the principle behind this and believes that the reason lies in the precise control of the mass ratio of alumina, binder, additives, dispersants, and auxiliaries, and the full utilization of their synergistic effects. This allows for the construction of a coating "skeleton" on the separator that combines excellent puncture resistance and high-temperature stability, while ensuring sufficient ion transport channels. This system effectively solves the problems of particle agglomeration and stability that easily occur in high-solids content slurries, thereby endowing the ceramic slurry with good coating processability and facilitating the formation of a uniform, defect-free ceramic coating. Furthermore, the high density of sulfonic acid groups on the surface of the sulfonated base film undergoes deep interfacial synergy with the functional components in the ceramic coating: the polar groups in the binder form a strong hydrogen bond network or acid-base ion crosslinking with the sulfonic acid groups; the additives act as "molecular bridges," condensing with the hydroxyl groups on the alumina surface at one end and chemically bonding with the sulfonic acid groups at the other end; and the mechanical interlocking formed by the coordination of Lewis acid sites on the alumina surface with the sulfonic acid groups and the excellent wetting and penetration of the ceramic slurry on the hydrophilic sulfonated surface significantly optimizes the interfacial adhesion between the ceramic coating and the sulfonated base film, and improves the stability under long-term electrochemical conditions. Ultimately, this can greatly enhance the puncture resistance of the separator and effectively reduce the zero-charge rate of the battery during production and use.

[0034] In one specific embodiment, the median particle size D50 of alumina is 1.0 μm to 2.0 μm. For example, the D50 of alumina can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2.0 μm. This particle size range is the cornerstone for constructing coatings that combine high strength, suitable pore structure, and excellent processability: it can form a uniform microstructure through dense particle packing, giving the ceramic coating excellent puncture resistance and high-temperature stability; it can also form an interconnected submicron-level pore network between particles, ensuring sufficient electrolyte wetting and efficient lithium-ion transport; and it can better coordinate with sulfonic acid groups, improving the interfacial adhesion of the ceramic coating on the sulfonated base film. Meanwhile, this scale effectively avoids the problem of poor slurry stability caused by the easy aggregation and difficulty in dispersion of nanoparticles, and also prevents the risk of uneven porosity and sedimentation caused by excessively large particles, so that the slurry has good rheological properties and coating applicability, and ultimately achieves the comprehensive goal of improving the safety of the separator, the yield of the battery and the electrochemical performance.

[0035] In one specific embodiment, the adhesive includes at least one of polyacrylamide, cyanoacrylate, cyanoacrylate-polyethylene glycol, and polyvinyl acetate. Polyacrylamide, through its abundant hydroxyl groups, forms a strong hydrogen bond network with the sulfonic acid groups on the surface of the sulfonated film, providing basic adhesion, interfacial adsorption, and good wettability. Cyanoacrylate can rapidly polymerize and cure, forming a highly cross-linked rigid framework, endowing the ceramic coating with excellent resistance to electrolyte swelling and interfacial durability. Simultaneously, its strongly electron-withdrawing cyano and ester groups not only act as hydrogen bond acceptors, binding with the sulfonic acid groups, but the cyanoacrylate monomers are also easily induced by the sulfonic acid groups to undergo rapid anionic polymerization, directly curing in situ on the surface of the sulfonated film to form covalent anchorage. The combination of cyanoacrylate and polyethylene glycol achieves a balance of rigidity and flexibility, significantly enhancing flexibility and ionic affinity while maintaining high strength. The ester groups in polyvinyl acetate can form stable hydrogen bonds with the sulfonic acid groups. Adding the above-mentioned binder to the ceramic slurry can construct a coating structure that combines high adhesion, suitable flexibility, excellent electrochemical stability and good process adaptability, thereby providing long-term reliable mechanical and interface protection for the ceramic separator and effectively improving battery safety and production yield.

[0036] In one specific embodiment, the additive includes at least one of sodium carboxymethyl cellulose, polyethylene glycol, sodium polyacrylate, and polyethylene oxide. Sodium polyacrylate ensures the primary dispersion of ceramic particles and the stability of the ceramic slurry through electrostatic and steric hindrance effects; sodium carboxymethyl cellulose, acting as a rheological architect, provides structural viscosity and pseudoplasticity, endowing the ceramic slurry with excellent coating processability and wet film forming ability; simultaneously, sodium carboxymethyl cellulose and sodium polyacrylate are rich in carboxylate anions, which can undergo strong acid-base neutralization reactions or ion exchange with the sulfonic acid groups on the surface of the sulfonated base film, forming a stable ion bridge or hydrogen bond network, effectively resisting the peeling stress caused by electrolyte swelling; the dense ether oxygen atoms on the main chains of polyethylene glycol and polyethylene oxide are excellent proton acceptors, capable of forming multiple hydrogen bond crosslinks with the active hydrogen in the sulfonic acid groups, not only enhancing the interfacial bonding force, but also their flexible long chains acting as stress buffers between rigid ceramic particles and the base film, preventing the propagation of interfacial microcracks. Adding the above-mentioned additives to the ceramic slurry solves the technical problems from slurry preparation and coating to the final coating performance, laying the material foundation for obtaining a uniform, tough, and electrochemically stable ceramic coating, thereby effectively improving the overall reliability of the diaphragm.

[0037] In one specific embodiment, the dispersant includes at least one of sodium hexametaphosphate, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfonate. Sodium hexametaphosphate, as an inorganic polyelectrolyte, forms strong adsorption on the particle surface through its multidentate phosphate ions and provides strong electrostatic repulsion, ensuring that the nanoparticles are monodisperse and penetrate deep into the micropores and rough structures of the sulfonated base film surface with the liquid phase, forming a strong mechanical interlock after drying. Hexadecyltrimethylammonium bromide, as a cationic surfactant, relies on its positively charged quaternary ammonium salt head group to adsorb onto the negatively charged particle surface and utilizes the steric hindrance generated by its long alkyl chain to achieve stability. Sodium dodecyl sulfonate, as an anionic surfactant, can significantly reduce the contact angle to achieve superspreading of the ceramic slurry by utilizing the homoionic compatibility between its sulfonate group and the sulfonic acid groups on the base film surface, ensuring close contact between the ceramic coating and the sulfonated base film. Adding the above-mentioned dispersant to the ceramic slurry can completely break down particle agglomeration, ensuring the high uniformity and storage stability of the ceramic slurry, laying the foundation for the subsequent formation of a defect-free high-performance ceramic coating, and ensuring that the ceramic coating can fully wet and embed into the microstructure of the base film, significantly enhancing the overall interfacial bonding strength.

[0038] In one specific embodiment, the additive is a surfactant that can significantly reduce the surface tension of the ceramic slurry, thereby producing wetting, penetration, emulsification, and dispersion functions. The additive includes at least one of polyoxyethylene, polyoxypropylene, pentylenetetroxide ether, polyoxyethylene fatty alcohol ether, and alkyl naphthalene sulfonate. Polyoxyethylene and polyoxyethylene fatty alcohol ether significantly improve the wetting and spreading properties of the ceramic slurry on the hydrophobic base film due to their hydrophilic segments, fundamentally eliminating defects such as coating pinholes; polyoxypropylene and pentylenetetroxide ether, relying on their hydrophobic properties, effectively eliminate and suppress foam generated in the ceramic slurry during stirring and transportation, ensuring a dense and non-porous ceramic coating; alkyl naphthalene sulfonate, as an anionic surfactant, provides auxiliary electrostatic stabilization. These additives can act on the gas-liquid and liquid-solid interfaces, effectively solving core process problems such as wetting, leveling, defoaming, and auxiliary stabilization in coating processing, and are essential guarantees for obtaining macroscopically uniform, defect-free, high-quality ceramic coatings.

[0039] In one specific embodiment, the sulfonated base membrane includes a sulfonated polypropylene separator and / or a sulfonated polyethylene separator. This application does not limit the specific parameters of the sulfonation treatment; hydrophilic sulfonic acid groups can be introduced onto the surface and within the pores of the polypropylene or polyethylene separator. For example, a direct sulfonation method can be used, where monomers already containing sulfonic acid groups or sulfonatable groups are copolymerized during the polypropylene / polyethylene synthesis stage, thereby directly introducing sulfonic acid groups into the main chain or side chain of the polypropylene / polyethylene, resulting in a sulfonated polypropylene separator or a sulfonated polyethylene separator. The sulfonic acid groups on the surface of the sulfonated base membrane have high reactivity, capable of forming strong hydrogen bonds or ionic bonds with the functional groups of the binder in the ceramic coating, and can also bond or coordinate with additives and alumina. Simultaneously, during ceramic slurry coating, its liquid phase components can partially penetrate into the micropores of the sulfonated base membrane, forming a robust physically interlocked structure after curing. This combination of chemical anchoring and physical interlocking prevents the ceramic coating from peeling off the smooth base membrane, ensuring the structural integrity of the ceramic separator during volume changes during battery charging and discharging. In addition, sulfonation transforms the originally hydrophobic polypropylene or polyethylene separator into a hydrophilic one, significantly improving the sulfonated membrane's ability to absorb and retain electrolyte, reducing the transport resistance of lithium ions within the separator, and significantly enhancing the battery's electrochemical performance.

[0040] In one specific embodiment, the degree of sulfonation of the sulfonated base film is 0.5% to 0.7%, for example, the degree of sulfonation of the sulfonated base film can be 0.5%, 0.55%, 0.6%, 0.65%, or 0.7%. The degree of sulfonation of the sulfonated base film of this application can be obtained by coulomb sulfur analyzer.

[0041] In one specific embodiment, the thickness of the sulfonated base film is 0.08 mm to 0.10 mm, for example, the thickness of the sulfonated base film can be 0.08 mm, 0.09 mm, 0.10 mm, etc. When the thickness of the sulfonated base film is within the above range, while satisfying the mechanical strength of the base film itself and providing stable support for the ceramic coating, the proportion of inactive materials is reduced to the maximum extent to improve the battery energy density. This thickness can also achieve good structural and process matching with the ceramic coating, ensuring the dimensional stability and flexibility of the ceramic separator. At the same time, the thinner base film is conducive to shortening the lithium-ion transport path and reducing internal resistance, while the rigid-flexible structure formed by it and the highly stable ceramic coating ensures that the separator still maintains excellent puncture resistance, thermal safety and dimensional integrity after overall thinning.

[0042] In one specific embodiment, the thickness of the ceramic coating is 2.5 μm to 4.5 μm, for example, the thickness of the ceramic coating can be 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, etc. When the thickness of the ceramic coating is within the above range, it is sufficient to form a continuous, tough, and highly porosity inorganic protective layer. While ensuring excellent puncture resistance, thermal safety, and electrolyte wettability, it avoids excessively increasing ion migration resistance, thus ensuring the high electrochemical performance of the battery. Moreover, this thickness is perfectly matched with the specified high solids content slurry system and conventional coating process, ensuring that the ceramic coating can be prepared efficiently and stably, and has excellent uniformity, adhesion, and flexibility.

[0043] In one specific embodiment, the ceramic slurry is prepared according to the following steps: According to the mass ratio, alumina is mixed with deionized water, and the pH value is adjusted to 3.5~4.5 to obtain an alumina suspension with a solid content of 25%~35%; the alumina suspension is then mixed with binders, additives, dispersants and auxiliaries to obtain ceramic slurry.

[0044] Specifically, alumina and deionized water are mixed in a predetermined ratio, and the pH of the mixture is precisely adjusted to a weakly acidic range of 3.5 to 4.5 to obtain an alumina suspension with a solid content of 25% to 35%. Binders, dispersants, additives, and other auxiliaries are added to the stabilized alumina suspension and thoroughly dispersed and mixed to finally obtain a homogeneous and stable ceramic slurry.

[0045] This application does not limit the specific parameters of the mixing process; it is sufficient to mix the components evenly.

[0046] This application does not limit the acid or alkali agent used to adjust the pH value of the alumina suspension. It can be selected according to actual needs, such as nitric acid, hydrochloric acid, sulfuric acid, etc.

[0047] The ceramic slurry preparation method provided in this application optimizes the performance of the ceramic slurry through a step-by-step construction strategy: First, the pH value is precisely adjusted to a weakly acidic range of 3.5~4.5, causing the alumina particles to be protonated and carrying a high-density positive charge. Strong electrostatic repulsion is used to achieve initial stable dispersion at a high solids content (25%~35%), laying the foundation for subsequent processing. Subsequently, functional components such as binders, additives, dispersants, and auxiliaries are introduced to further enhance stability through steric hindrance effects and synergistically regulate the rheological properties of the ceramic slurry and the microstructure of the ceramic coating. This ultimately forms a composite ceramic coating with high mechanical strength, rich porous structure, and excellent electrolyte wettability, thereby effectively improving the puncture resistance, thermal stability, and ionic conductivity of the ceramic diaphragm. This method starts from the chemical regulation of the particle surface and achieves synergistic optimization of dispersion stability, coating processability, and final electrochemical performance through precise design of process steps.

[0048] In one specific embodiment, the diaphragm is prepared according to the following steps: A ceramic slurry is coated on at least one side of the sulfonated base membrane and dried to obtain a diaphragm; wherein the drying temperature is 50℃~90℃ and the drying time is 10min~40min.

[0049] For example, the drying temperature for drying treatment can be 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc., and the drying time can be 10min, 15min, 20min, 25min, 30min, 35min, 40min, etc.

[0050] The membrane preparation method of this application can ensure that the ceramic coating is uniformly loaded on the surface of the sulfonated base film, thereby ensuring the structural integrity of the ceramic coating, the interfacial bonding strength between the ceramic coating and the sulfonated base film, and ultimately reducing the zero charge rate of the battery.

[0051] This application also provides a battery including the aforementioned separator. This battery exhibits a low zero charge rate.

[0052] In one specific embodiment, the battery of this application further includes a positive electrode sheet, which includes a positive current collector and a positive electrode coating coated on the positive current collector. The positive electrode coating includes a positive electrode active material, which includes β-type nickel hydroxide.

[0053] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes nickel foam, porous nickel-plated steel strip, etc.

[0054] In one specific embodiment, the positive electrode coating further includes a conductive agent and a binder. The conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and vapor-grown carbon fiber (VGCF). The binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, polyvinylidene fluoride, and polytetrafluoroethylene.

[0055] In one specific embodiment, the battery of this application further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode coating coated on the negative electrode current collector. The negative electrode coating includes a negative electrode active material, which includes a hydrogen storage alloy.

[0056] In this application, there is no particular limitation on the type of negative electrode current collector; it can be any known material suitable for use as a negative electrode current collector. In one embodiment, the negative electrode current collector includes nickel foam, porous nickel-plated steel strip, etc.

[0057] In one specific embodiment, the negative electrode coating further includes a conductive agent and a binder. The conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and vapor-grown carbon fiber (VGCF). The binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, polyvinylidene fluoride, and polytetrafluoroethylene.

[0058] In one specific embodiment, the battery of this application further includes an electrolyte, which is an electrolyte known in the art that can be used in nickel-metal hydride batteries and makes the battery's electrochemical performance excellent, including potassium hydroxide solution, and can be specifically set as needed.

[0059] In one embodiment, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte.

[0060] In one specific embodiment, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0061] This application does not impose any particular restrictions on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape.

[0062] This application does not impose any particular restrictions on the application fields of nickel-metal hydride batteries, and they can be used in fields such as consumer batteries, power batteries for new energy vehicles, and energy storage batteries.

[0063] The present application will be further described in detail below through specific embodiments.

[0064] Example 1 1. Preparation of ceramic diaphragms Alumina was mixed with water, and the pH was adjusted to 4 to obtain an alumina suspension with a solid content of 30%. Then, polyacryl alcohol, sodium carboxymethyl cellulose, sodium hexametaphosphate, and polyoxyethylene were added to the alumina suspension and mixed evenly to obtain a ceramic slurry.

[0065] A ceramic slurry was uniformly coated on one surface of a sulfonated polypropylene diaphragm with a thickness of 0.08 mm, and then dried. The above operation was then repeated on the other surface of the sulfonated polypropylene diaphragm to obtain the diaphragm.

[0066] The ceramic slurry was formulated with the following mass ratios: 25% alumina, 2.5% polyacrylamide, 0.8% sodium carboxymethyl cellulose, 0.8% sodium hexametaphosphate, 0.05% polyethylene oxide, and the remainder being deionized water; the alumina had a D50 of 1.5 μm; the sulfonated polypropylene diaphragm had a sulfonation degree of 0.6% and a ceramic coating thickness of 3.5 μm; the drying temperature was 70℃ and the drying time was 25 min.

[0067] 2. Preparation of the positive electrode sheet The positive electrode active material β-type nickel hydroxide, conductive graphite, and polymethyl methacrylate binder were mixed evenly at a mass ratio of 98.5:1:0.5 and thoroughly stirred in a relevant solvent to prepare a positive electrode slurry with a solid content of 80%. The positive electrode slurry was uniformly coated onto pre-pressed nickel foam, dried at 75°C, and then rolled to obtain a positive electrode sheet with a thickness of 460 μm. After softening, the positive electrode sheet was cut into 50 mm × 120 mm dimensions, and tabs were spot-welded for later use.

[0068] 3. Preparation of electrolyte Take appropriate amounts of potassium hydroxide, sodium hydroxide, and lithium hydroxide, add a certain amount of pure water, stir well, and let cool before use.

[0069] 4. Preparation of negative electrode sheet Hydrogen storage alloy (anode active material), conductive graphite, and polyimide binder were mixed uniformly at a mass ratio of 98.5:1:0.5 and thoroughly stirred in a relevant solvent to prepare a cathode slurry with a solid content of 90%. The cathode slurry was uniformly coated onto a nickel-plated steel strip, dried at 75°C, and then rolled to obtain a cathode sheet with a thickness of 210 μm. After softening, the cathode sheet was cut into 50 mm × 150 mm dimensions for later use.

[0070] 5. Battery manufacturing The positive and negative electrode sheets are stacked in sequence, and the stacked electrode sheets are wound with a ceramic separator to obtain an electrode assembly. The electrode assembly is placed in a pre-formed aluminum-plastic film and dehydrated at 80°C. The prepared electrolyte is then injected, and the battery undergoes vacuum sealing, settling, formation, and shaping processes to obtain the AA2600 nickel-metal hydride battery.

[0071] The main differences between Examples 2-56 and Comparative Examples 2-11 and Example 1 are the parameters of the ceramic slurry and the diaphragm, as shown in Tables 1 and 2.

[0072] Comparative Example 1 The difference between this comparative example and Example 1 is that the diaphragm used is a sulfonated base membrane without ceramic coating.

[0073] Table 1

[0074] Table 2

[0075] Test case Zero-power test Preparation before testing: 1. Ensure the battery is at zero voltage (short-circuit discharge to 0V). 2. Prepare a charging tester and a voltage recorder. Test steps: 1. Charge with currents of 1A, 2A, and 3A for 5 seconds, 10 seconds, and 25 seconds respectively; 3. Record the voltage change after charging. If the voltage quickly returns to the normal value (e.g., 1.2V), it indicates no short circuit; if the voltage does not change or rises slowly, there is a short circuit.

[0076] The methods for zero-charge testing for winding, sealing, and formation are described above. The three zero-charge rates represent the zero-charge rates at different stages of the battery manufacturing process.

[0077] Table 3

[0078] As shown in Table 3, based on the comparison between Examples 1-56 and Comparative Example 1, it can be seen that when the membrane surface is coated with ceramic slurry, the puncture resistance of the membrane is improved, which can reduce the zero charge rate of the nickel-metal hydride battery.

[0079] According to the comparison of Examples 1-4, 5-7, 8-10, 11-13, 14-16 and Comparative Examples 2-3, 4-5, 6-7, 8-9, 10-11, it can be seen that when the ceramic slurry is composed of 15%-40% alumina, 1.0%-3.0% binder, 0.2%-1.2% additives, 0.2%-1.2% dispersant, 0.02%-0.2% auxiliary agent, and the balance being water, a coating with excellent puncture resistance and high-temperature stability can be constructed on the separator, while ensuring sufficient ion transport channels and reducing the zero-charge rate of the battery.

[0080] According to the comparison of Examples 1, 17-20, when the median particle size D50 of alumina is 1.0-2.0 μm, alumina can participate in the formation of a ceramic coating with excellent puncture resistance, thereby reducing the zero charge rate of the battery.

[0081] As can be seen from the comparison of Examples 1, 21-23, and 33, when at least one of polyacrylol, cyanoacrylate, cyanoacrylate-polyethylene glycol, and polyvinyl chloride is selected as the binder, the ceramic separator has excellent adhesion, flexibility, and electrochemical stability, thereby improving the safety performance of the battery.

[0082] According to the comparison of Examples 1, 24-26, and 34, when at least one of sodium carboxymethyl cellulose, polyethylene glycol, sodium polyacrylate, and polyethylene oxide is selected as the additive, it is beneficial to reduce the zero-point rate of the battery.

[0083] As can be seen from the comparison of Examples 1, 27-28, and 35, when at least one of sodium hexametaphosphate, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfonate is selected as the dispersant, the battery can exhibit excellent safety.

[0084] According to the comparison of Examples 1, 29-32, and 36, when at least one of polyoxyethylene, polyoxypropylene, pentylenetetrazol ether, polyoxyethylene fatty alcohol ether, and alkyl naphthalene sulfonate is selected as the additive, the uniformity and storage stability of the ceramic slurry are better, which is conducive to the coating of the ceramic coating on the base film, thereby effectively improving the safety of the battery.

[0085] Based on the comparison of Examples 1 and 37-39, it can be seen that when the pH value of the alumina suspension is 3.5-4.5, it helps the stability of the slurry coating, thereby reducing the zero-charge rate of the battery.

[0086] According to the comparison of Examples 1, 40-42, when the solid content of the alumina suspension is 25%-35%, the battery can exhibit a low zero charge rate.

[0087] According to the comparison of Examples 1, 43-45, the degree of sulfonation of the sulfonated base film is 0.5%-0.7%, and the zero charge rate of the battery can be effectively reduced.

[0088] As can be seen from the comparison of Examples 1, 46-48, the thickness of the sulfonated base film is 0.08mm-0.10mm, which enables the battery to achieve both high energy density and high safety.

[0089] As can be seen from the comparison of Examples 1, 49-53, the thickness of the ceramic coating is 2.5μm to 4.5μm, which enables the battery to exhibit excellent electrochemical performance and safety performance.

[0090] According to the comparison of Examples 1 and 54-56, the drying temperature of the drying treatment is 50℃~90℃ and the drying time is 10min~40min, which is beneficial to improve the structural integrity of the ceramic coating and the interfacial bonding strength between the ceramic coating and the sulfonated base film, and reduce the zero charge rate of the battery.

[0091] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A diaphragm, characterized in that, The diaphragm comprises a sulfonated base membrane and a ceramic coating coated on at least one side of the sulfonated base membrane. The ceramic slurry used to form the diaphragm coating comprises the following components by mass percentage: 15%~40% alumina, 1.0%~3.0% binder, 0.2%~1.2% additives, 0.2%~1.2% dispersant, 0.02%~0.2% auxiliary agent, and the balance being water.

2. The diaphragm according to claim 1, characterized in that, The median particle size D50 of the alumina is 1.0 μm to 2.0 μm.

3. The diaphragm according to claim 1, characterized in that, The adhesive includes at least one of polyacryl alcohol, cyanoacrylate, cyanoacrylate-polyethylene glycol, and polyvinyl chloride.

4. The diaphragm according to claim 1, characterized in that, The additives include at least one of sodium carboxymethyl cellulose, polyethylene glycol, sodium polyacrylate, and polyethylene oxide.

5. The diaphragm according to claim 1, characterized in that, The dispersant comprises at least one of sodium hexametaphosphate, hexadecyltrimethylammonium bromide, and sodium dodecyl sulfonate; and / or, The additives include at least one of polyoxyethylene, polyoxypropylene, pentylenetetrazol ether, polyoxyethylene fatty alcohol ether, and alkyl naphthalene sulfonate.

6. The diaphragm according to claim 1, characterized in that, The sulfonated base membrane includes a sulfonated polypropylene separator and / or a sulfonated polyethylene separator; and / or, The degree of sulfonation of the sulfonated base film is 0.5%~0.7%.

7. The diaphragm according to claim 1, characterized in that, The thickness of the sulfonated base film is 0.08 mm to 0.10 mm; and / or, The thickness of the ceramic coating is 2.5μm to 4.5μm.

8. The diaphragm according to claim 1, characterized in that, The ceramic slurry is prepared according to the following steps: According to the mass ratio, the alumina is mixed with deionized water, and the pH value is adjusted to 3.5~4.5 to obtain an alumina suspension with a solid content of 25%~35%. The alumina suspension is mixed with the binder, the additive, the dispersant, and the auxiliary agent to obtain the ceramic slurry.

9. The diaphragm according to claim 8, characterized in that, The diaphragm is prepared according to the following steps: The ceramic slurry is coated onto at least one side of the sulfonated base membrane and then dried to obtain the diaphragm. The drying temperature of the drying process is 50℃~90℃, and the drying time is 10min~40min.

10. A battery, characterized in that, The battery includes the separator according to any one of claims 1 to 9.

Images