Photocurable composite lithium battery separator, method for preparing the same, and battery

Abstract

This invention relates to the field of battery technology, and proposes a photocurable composite lithium battery separator, its preparation method, and a battery thereof. The photocurable composite lithium battery separator includes a base film and a composite coating disposed on at least one surface of the base film; the raw materials of the composite coating include porous ceramic powder, a fully aromatic multi-component copolymer polyacrylate resin, and a photoinitiator; the glass transition temperature of the fully aromatic multi-component copolymer polyacrylate resin is 270~300℃. Through the above technical solution, the problems of high-temperature shrinkage and poor ionic conductivity of lithium battery separators in related technologies are solved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a photocurable composite lithium battery separator, its preparation method, and the battery thereof. Background Technology

[0002] As a core component of lithium-ion batteries, the separator plays a crucial role in electronic insulation, ion conduction, electrolyte storage, and safety protection. However, traditional polyolefin separators suffer from problems such as low surface energy, poor electrolyte wettability, and insufficient electrolyte retention capacity. Furthermore, they are prone to thermal shrinkage and thermal melting under high-temperature conditions, severely limiting the battery's fast-charging performance, cycle life, and safety.

[0003] In existing ceramic-coated separators, the adhesives used are mostly conventional types such as water-based acrylates or polytetrafluoroethylene (PVDF) systems. These adhesives begin to soften at relatively low temperatures, leading to shrinkage, deformation, powdering, and delamination of the coating at high temperatures, failing to meet the requirements for battery use under extreme conditions above 150°C. Furthermore, conventional polymer adhesives themselves have poor stability, easily swelling when immersed in electrolyte, making it difficult to balance heat resistance and wettability. In addition, the interfacial adhesion between existing adhesives and the inorganic powders and base film in the coating is also poor, easily leading to interfacial delamination during long-term cycling, resulting in interruption of ion conduction pathways and a significant reduction in cycle life.

[0004] On the other hand, the ceramic powders commonly used in existing ceramic-coated separators are mostly dense powders such as alumina and boehmite. These powders, when accumulated, easily form numerous closed pores, lengthening the electrolyte wetting path, increasing resistance, and limiting the improvement in wetting rate. Simultaneously, the low pore volume of ceramic powders limits electrolyte storage, making them prone to localized electrolyte shortages and increased polarization during high-rate discharge. Furthermore, the lack of a interconnected pore system in the powder prevents the construction of efficient lithium-ion transport pathways, further restricting the battery's fast-charging performance.

[0005] In the current process of preparing lithium battery separators, thermal curing is commonly used. However, this method has low drying efficiency at high temperatures, making it difficult to meet the rapid demands of high-speed winding production. Furthermore, the base film, especially polyolefin base film, is prone to thermal shrinkage during thermal curing, leading to overall dimensional instability of the separator and consequently affecting cell assembly and safety performance.

[0006] To address the aforementioned technical issues, there is an urgent need to develop a composite coating membrane that combines ultrafast electrolyte wetting, high heat resistance and dimensional stability, strong interfacial bonding ability, and high ionic conductivity. Summary of the Invention

[0007] This invention proposes a photocurable composite lithium battery separator, its preparation method, and the battery thereof, to solve or alleviate at least one of the above-mentioned problems.

[0008] The technical solution of the present invention is as follows: This invention proposes a photocurable composite lithium battery separator, comprising a base film and a composite coating disposed on at least one surface of the base film; The raw materials for the composite coating include porous ceramic powder, fully aromatic multi-component copolyacrylate resin, and photoinitiator; The glass transition temperature of the fully aromatic multi-component copolymer polyacrylate resin is 270~300℃.

[0009] Preferably, the mass ratio of the porous ceramic powder to the fully aromatic multi-component copolyacrylate resin is 50~85:12~40; The porous ceramic powder has a pore size distribution of 2~50nm and a specific surface area of ​​80~200m². 2 / g.

[0010] Preferably, the raw materials for the fully aromatic multi-component copolyacrylate resin include functional monomers and initiators in a weight ratio of 100:1.2~1.5.

[0011] Preferably, the functional unit is functional unit I, functional unit II, functional unit III, and functional unit IV; The functional monomer I includes one or more of bisphenol A dimethacrylate, bisphenol S dimethacrylate, and biphenyl dimethacrylate; The functional monomer II includes one or both of N-phenylmaleimide and N-benzylmaleimide; The functional monomer III includes one or more of the following: isocyanate-containing functional monomers, hydroxyl-containing functional monomers, and epoxy-containing functional monomers. The functional monomer IV includes one or more of trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate.

[0012] Preferably, the functional unit is functional unit I, functional unit II, or functional unit IV; The functional monomer I includes one or more of 9,9-diphenylfluorenyl methacrylate, styrene, and methylstyrene; The functional monomer II includes one or both of N-cyclohexylmaleimide and N-phenylmaleimide; The functional monomer IV includes one or both of neopentyl glycol diacrylate and 1,6-hexanediol diacrylate.

[0013] Preferably, the preparation method of the fully aromatic multi-component copolyacrylate resin includes the following steps: The functional monomer is dissolved in solvent I, the initiator is added, and the reaction is carried out to obtain the fully aromatic multi-component copolyacrylate resin.

[0014] Preferably, the thickness of the composite coating on one side is 1~5μm.

[0015] Preferably, the raw materials for the composite coating further include dispersants and leveling agents; The weight ratio of the porous ceramic powder, the fully aromatic multi-component copolymer polyacrylate resin, the photoinitiator, the dispersant, and the leveling agent is 50~85:12~40:0.5~3:0.3~2:0.1~1.

[0016] This invention also proposes a method for preparing a photocurable composite lithium battery separator, comprising the following steps: The raw materials for the composite coating are mixed to obtain a coating slurry; The coating slurry is coated on one or both sides of the base film, cured, and dried to obtain the photocurable composite lithium battery separator.

[0017] The present invention also proposes a battery comprising the aforementioned photocurable composite lithium battery separator or the photocurable composite lithium battery separator prepared by the aforementioned preparation method.

[0018] The beneficial effects of this invention are as follows: In this invention, a fully aromatic multi-component copolymer polyacrylate resin with a glass transition temperature of 270~300℃ is used in the composite coating of lithium battery separators. It exhibits excellent coating properties for ceramic particles and interfacial adhesion with the base film, while also possessing good resistance to swelling and oxidative decomposition. This solves the problems of conventional adhesives used in lithium battery separator coatings, such as easy softening and deformation at high temperatures, poor thermal shrinkage, and powdering and delamination. Furthermore, under the action of a photoinitiator, the active groups on the resin side chains rapidly undergo free radical cross-linking reactions, solidifying to form a high-density three-dimensional cross-linked network structure. This effectively improves the high-temperature dimensional stability of the lithium battery separator, thereby effectively enhancing its structural stability and heat resistance, resulting in a transverse thermal shrinkage rate of ≤2.3% and a longitudinal thermal shrinkage rate of ≤1.8% at 150℃. Detailed Implementation

[0019] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will be described through embodiments.

[0021] A specific embodiment of the first aspect of the present invention provides a photocurable composite lithium battery separator, comprising a base film and a composite coating disposed on at least one surface of the base film; The raw materials for the composite coating include porous ceramic powder, fully aromatic multi-component copolymer polyacrylate resin, and photoinitiator; The glass transition temperature of fully aromatic multi-component copolymer polyacrylate resins is 270~300℃.

[0022] In this invention, the photocurable composite lithium battery separator includes a base film and a composite coating on the surface of the base film. The base film serves as the main supporting framework of the separator, preventing short circuits caused by direct contact between the positive and negative electrodes, and also providing structural strength support for the separator. The base film can be any type of base film used in lithium battery separators in the art, such as a polyolefin base film, a polyimide base film, a polyethylene terephthalate base film, a polyarylamide base film, or a polyetherimide base film, preferably a polyolefin base film. Polyolefin base films themselves have a microporous structure, good ionic conductivity, low manufacturing cost, and mature technology, making them the most widely used base films for lithium battery separators. Polyolefin base films can be, for example, polyethylene base films or polypropylene base films, preferably polyethylene base films. The thickness of the base film can be 6~15μm, for example, any value or range between any two values ​​from 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, to 15μm.

[0023] In this invention, the composite coating of the photocurable composite lithium battery separator uses a fully aromatic multi-component copolymer polyacrylate resin with a high glass transition temperature. It is not prepared from conventional aliphatic acrylates, soft-segment acrylates, or simple physical compounding. Its molecular backbone and side chains incorporate large-volume aromatic rings, fused rings, and heat-resistant heterocyclic structures, exhibiting extremely weak chain segment mobility and excellent heat resistance and dimensional stability at high temperatures. Differential scanning calorimetry (DSC) analysis shows its glass transition temperature (Tg) to be 270~300℃, for example, 270℃, 275℃, 282℃, 295℃, or 300℃.

[0024] In this invention, a photoinitiator is added to the composite coating. Under irradiation, the photoinitiator absorbs light energy and rapidly generates active free radicals, causing cross-linking of the components within the coating and achieving curing of the composite coating in a short time. The photoinitiator can be any photoinitiator in the art, such as a free radical photoinitiator or a cationic photoinitiator; free radical photoinitiators can be, for example, α-hydroxyketone photoinitiators or acylphosphine oxide photoinitiators; α-hydroxyketone photoinitiators can be, for example, 1-hydroxycyclohexylphenyl ketone (photoinitiator 184) or 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator 1173); acylphosphine oxide photoinitiators can be, for example, 2,4,6-trimethylbenzoyl diphenylphosphine oxide (photoinitiator TPO) or phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator 819). In this invention, the photoinitiator is preferably one or more of photoinitiator 184, photoinitiator TPO, and photoinitiator 819.

[0025] In this invention, porous ceramic powder can construct electrolyte transport and storage channels within the composite coating, significantly improving the wetting rate, electrolyte retention capacity, and ion conduction efficiency of the lithium battery separator. Unlike traditional ceramic powders that rely solely on interparticle spacing for electrolyte conduction, this invention overcomes the technical bottleneck of insufficient electrolyte wetting at the material structure level. Simultaneously, it ensures the coating possesses high porosity and good mechanical support, without clogging the separator's transport channels, thus meeting the requirements of high-rate, long-cycle lithium-ion batteries. The porous ceramic powder can be any porous ceramic powder in the art, such as porous alumina, porous boehmite, porous silica, or porous zirconium oxide, preferably porous alumina.

[0026] In one embodiment of the present invention, the mass ratio of porous ceramic powder to fully aromatic multi-component copolyacrylate resin is 50~85:12~40. The porous ceramic powder has a pore size distribution of 2~50nm, for example, it can be any two values ​​between 2~20nm, 2~50nm, 5~30nm, and 10~50nm, and its specific surface area is 80~200m². 2 / g, for example, could be 80m 2 / g, 100m 2 / g、120m 2 / g, 140m 2 / g, 150m 2 / g、160m 2 / g、180m 2 The range of any point value in / g and any two point values ​​is preferably 150m. 2 / g、180m 2 / g.

[0027] In this invention, the mass ratio of porous ceramic powder to fully aromatic multi-component copolyacrylate resin is 50~85:12~40, the pore size distribution of the porous ceramic powder is 2~50 nm, and the specific surface area is 80~200 m². 2 By adjusting the mass ratio of porous ceramic powder and fully aromatic multi-component copolyacrylate resin in the composite coating, and limiting the pore size distribution and specific surface area of ​​the porous ceramic powder, the cured fully aromatic multi-component copolyacrylate resin can form a uniform film in the composite coating without agglomeration, clogging of ceramic powder pores, or excessive coating thickness. This effectively preserves the pore structure of the ceramic powder, maximizing the maintenance of high porosity and high ion conduction channels in the coating, ensuring rapid, stable, and efficient conduction of lithium ions within the coating, and achieving a balance between high ion conductivity and high heat resistance.

[0028] In one embodiment of the present invention, the raw materials for the fully aromatic multi-component copolyacrylate resin include functional monomers and initiators in a weight ratio of 100:1.2~1.5.

[0029] In one embodiment of the present invention, the functional unit includes at least three of functional unit I, functional unit II, functional unit III, and functional unit IV. For example, the functional unit is functional unit I, functional unit II, and functional unit III, or the functional unit is functional unit I, functional unit II, or functional unit IV, or the functional unit is functional unit I, functional unit III, and functional unit IV, or the functional unit is functional unit I, functional unit II, functional unit III, and functional unit IV.

[0030] In this invention, among the functional monomers used to prepare the fully aromatic multi-component copolymer polyacrylate resin, functional monomer I serves as the core skeleton monomer of the fully aromatic multi-component copolymer polyacrylate resin. Its molecular structure contains large-volume conjugated aromatic ring structures such as benzene rings and biphenyl rings, exhibiting significant steric hindrance and hindered molecular chain rotation. This significantly increases the glass transition temperature of the resin, endowing the diaphragm coating with high-temperature creep resistance, softening resistance, and dimensional stability. Simultaneously, the aromatic ring structure possesses excellent chemical stability and mechanical strength, improving the coating's resistance to electrolyte swelling and abrasion, preventing high-temperature deformation and peeling. Functional monomer I can be, for example, bisphenol A dimethacrylate, bisphenol S dimethacrylate, biphenyl-type dimethacrylate, 9,9-diphenylfluorenyl methacrylate, styrene, or methylstyrene.

[0031] In this invention, among the functional monomers used to prepare the fully aromatic multi-component copolymer polyacrylate resin, functional monomer II contains a maleimide heterocyclic rigid structure, which has a high thermal decomposition temperature and good thermal stability. When used in combination with functional monomer I, it can further improve the Tg value of the fully aromatic multi-component copolymer polyacrylate resin. The maleimide heterocyclic groups can enhance the intermolecular chain forces, improve the interfacial bonding force between the composite coating and the ceramic powder and base film, solve the problems of coating powdering and delamination, and simultaneously improve the aging resistance and oxidation resistance of the composite coating. Functional monomer II can be, for example, N-methylmaleimide, N-phenylmaleimide, N-benzylmaleimide, or N-cyclohexylmaleimide.

[0032] In this invention, the functional monomer III used to prepare the fully aromatic multi-component copolyacrylate resin is specifically a hard monomer containing polar active functional groups. These active functional groups can be, for example, isocyanate groups, hydroxyl groups, epoxy groups, carboxyl groups, and thiol groups. Introducing polar active functional groups into the molecular chain of the fully aromatic multi-component copolyacrylate resin can, on the one hand, improve the dispersibility and emulsification of the resin in a water-alcohol solvent system, ensuring a uniform and stable coating slurry; on the other hand, the active functional groups can form hydrogen bonds and chemical bonds with the hydroxyl groups on the surface of the ceramic powder in the composite membrane, thereby improving the interfacial adhesion between the resin and the ceramic particles; furthermore, the active functional groups can participate in the photocrosslinking reaction, increasing the crosslinking density of the composite coating, thereby improving the internal structural stability of the composite coating. In this invention, functional monomer III can be, for example, an isocyanate-containing hard monomer, a hydroxyl-containing hard monomer, or an epoxy-containing hard monomer. The isocyanate-containing hard monomer can be, for example, ethyl isocyanate methacrylate or tricyclooxypropyl isocyanate acrylate; the hydroxyl-containing hard monomer can be, for example, hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl methacrylate; and the epoxy-containing hard monomer can be, for example, glycidyl methacrylate or allyl glycidyl ether.

[0033] In this invention, the functional monomer IV used to prepare the fully aromatic multi-component copolyacrylate resin contains two or more unsaturated acrylate double bonds. Introducing this into the fully aromatic multi-component copolyacrylate resin allows the unsaturated acrylate double bonds to act as crosslinking bridging points during the photocuring of the composite coating, rapidly curing to form a high-density three-dimensional crosslinked network, shortening the curing time and improving curing efficiency. Simultaneously, the introduction of functional monomer IV increases the crosslinking density and mechanical strength of the coating, reduces the swelling rate of the diaphragm coating, avoids high-temperature creep of the diaphragm coating, and ensures that the coating does not clog the pores of the porous ceramic powder, maintaining efficient ion transport. In this invention, functional monomer IV can be, for example, trimethylolpropane triacrylate, pentaerythritol tetraacrylate, or ethoxylated trimethylolpropane triacrylate.

[0034] In one embodiment of the present invention, the functional monomers are functional monomer I, functional monomer II, functional monomer III, and functional monomer IV; The functional monomer I includes one or more of bisphenol A dimethacrylate, bisphenol S dimethacrylate, and biphenyl dimethacrylate; The functional monomer II includes one or both of N-phenylmaleimide and N-benzylmaleimide; The functional monomer III includes one or more of the following: isocyanate-containing functional monomers, hydroxyl-containing functional monomers, and epoxy-containing functional monomers. The functional monomer IV includes one or more of trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate.

[0035] In one embodiment of the present invention, the weight ratio of functional monomer I, functional monomer II, functional monomer III, and functional monomer IV is 60~70:10~15:15~20:5, for example, it can be 60:15:20:5, 65:15:15:5, 66:11:18:5, 70:10:15:5, and preferably 60:15:20:5.

[0036] In one embodiment of the present invention, the functional unit is functional unit I, functional unit II, and functional unit IV; The functional monomer I includes one or more of 9,9-diphenylfluorenyl methacrylate, styrene, and methylstyrene, preferably 9,9-diphenylfluorenyl methacrylate and styrene, more preferably 9,9-diphenylfluorenyl methacrylate and styrene in a weight ratio of 11:4. The functional monomer II includes one or both of N-cyclohexylmaleimide and N-phenylmaleimide; The functional monomer IV includes one or both of neopentyl glycol diacrylate and 1,6-hexanediol diacrylate.

[0037] In one embodiment of the present invention, the weight ratio of functional monomer I, functional monomer II, and functional monomer IV is 65~75:15~20:5~15, for example, it can be 65:20:15, 68:19:13, 75:15:10, 75:20:5, preferably 75:15:10.

[0038] In one embodiment of the present invention, the preparation method of the fully aromatic multi-component copolyacrylate resin includes the following steps: The functional monomer is dissolved in solvent I, an initiator is added, and the reaction is carried out to obtain a fully aromatic multi-component copolyacrylate resin.

[0039] In this invention, a fully aromatic multi-component copolyacrylate resin is prepared by solution free radical copolymerization. The functional monomers and initiator are stirred until completely dissolved to obtain a mixture. This mixture is then transferred to a reactor containing solvent I under a protective gas atmosphere. During the transfer, the mixture is added to the reactor at a uniform and stable rate over 3-3.5 hours, with the dropping rate controlled to ensure a smooth reaction and prevent vigorous polymerization, gelation, or excessively wide molecular distribution of the functional monomers. After the mixture is added, the mixture is heated to a reaction temperature of 80-85°C under a protective gas atmosphere and reacted for 5-6 hours. During the reaction, the initiator decomposes thermally, generating free radicals. These free radicals interact with the functional monomers to gradually form copolymer chains. After the reaction is complete, the reaction system is naturally cooled to room temperature. Residual unreacted monomers, low-molecular-weight polymers, and some solvent are then removed from the system, ultimately yielding a fully aromatic multi-component copolyacrylate resin rich in active functional groups. The molecular chain of fully aromatic multi-component copolyacrylate resin has active cross-linking sites. During the photocuring process of the composite coating, the active free radicals generated by the photoinitiator promote the rapid free radical cross-linking polymerization of the active groups of the side chains and end groups of the fully aromatic multi-component copolyacrylate resin, forming a three-dimensional network cross-linking structure, and finally achieving instantaneous curing of the composite coating, thereby endowing the coating with good heat resistance and structural stability.

[0040] In this invention, the protective gas used in the preparation process of the fully aromatic multi-component copolyacrylate resin can be any gas that can play a protective role in the art, such as nitrogen, helium, or argon, with nitrogen being preferred. The reaction temperature in the preparation process of fully aromatic multi-component copolyacrylate resin is 80~85℃; the reaction time is 5~6h, for example, it can be any value among 5h, 5.5h, and 6h, or any range between any two values; under this reaction temperature and reaction time, the functional monomers can be fully polymerized and the conversion rate can be maximized.

[0041] In this invention, during the preparation of the fully aromatic multi-component copolyacrylate resin, solvent I can be any one or more solvents that disperse the functional monomers and initiators, such as methanol, ethanol, isopropanol, propylene glycol methyl ether acetate, acetone, methyl isobutyl ketone, and cyclohexanone. Preferably, it is a mixed solvent of cyclohexanone and propylene glycol methyl ether acetate in any volume ratio, or a mixed solvent of methyl isobutyl ketone and cyclohexanone in any volume ratio. More preferably, it is a mixed solvent of cyclohexanone and propylene glycol methyl ether acetate in a volume ratio of 1:1, or a mixed solvent of methyl isobutyl ketone and cyclohexanone in a volume ratio of 3:2.

[0042] In one embodiment of the present invention, the raw materials for the composite coating also include a dispersant and a leveling agent.

[0043] In this invention, the dispersant can make the components in the coating slurry uniform and stable, thereby ensuring the uniformity and stability of the composite coating formed during the coating process. The dispersant can be any dispersant in the art, such as polyacrylate dispersants, phosphate dispersants, or ammonium carboxylate dispersants.

[0044] In this invention, the leveling agent can reduce the surface tension of the coating slurry system, promote the rapid spreading of the coating slurry on the base film surface, and ensure that the coating thickness on the base film remains consistent. The leveling agent can be any leveling agent in the art, such as polyether modified silicone leveling agent, acrylate leveling agent, or fluorocarbon leveling agent.

[0045] In one embodiment of the present invention, the weight ratio of porous ceramic powder, fully aromatic multi-component copolymer polyacrylate resin, photoinitiator, dispersant, and leveling agent is 50~85:12~40:0.5~3:0.3~2:0.1~1, for example, it can be 50:12:0.5:0.3:0.1, 75:22:1.5:1.2:0.3, 80:17:1.2:1.0:0.3, 82:15:1.0:1.5:0.2, 70:25:1.8:0.8:0.2, 78:20:1.5:0.8:0.4, 85:40:3:2:1.

[0046] A second aspect of the present invention provides a method for preparing a photocurable composite lithium battery separator, used to prepare the photocurable composite lithium battery separator provided in the first aspect of the present invention, comprising the following steps: The raw materials for the composite coating are mixed to obtain a coating slurry; The coating slurry is applied to one or both sides of the base film, cured, and dried to obtain a photocurable composite lithium battery separator.

[0047] In one embodiment of the present invention, a method for preparing a photocurable composite lithium battery separator includes the following steps: Porous ceramic powder and dispersant are added to solvent II and dispersed. Then, fully aromatic multi-component copolymer polyacrylate resin, photoinitiator and leveling agent are added and mixed to obtain coating slurry. The coating slurry is applied to one or both sides of the base film, cured, and dried to obtain a photocurable composite lithium battery separator.

[0048] Traditional processes often use single-boiling-point solvents, which cannot simultaneously meet the dissolution and film-forming requirements of polymer components in the system. Low-boiling-point solvents dry too quickly, easily causing pinholes, while high-boiling-point solvent residues lead to coating stickiness, solvent contamination, and insufficient film surface smoothness. In addition, single-solvent systems cannot effectively regulate surface tension gradients, easily causing problems such as pinholes and flow marks, affecting coating consistency and mass production yield. In this invention, solvent II is a water-alcohol dual-solvent system, a mixed solvent formed by water and low-carbon alcohol solvents. The synergistic use of water and low-carbon alcohols can effectively achieve uniform dispersion of the fully aromatic multi-component copolymer polyacrylate resin, ensuring the stability of the coating slurry. At the same time, the use of water and low-carbon alcohols can regulate the evaporation rate of the coating slurry. The synergy of the two allows the composite coating to dry gradually, avoiding problems such as film surface cracking and base film curling caused by excessively rapid drying in lithium battery separators, and preventing problems such as solvent residue and film surface stickiness caused by excessively slow drying. In this invention, the low-carbon alcohol includes one or more of ethanol, isopropanol, and n-propanol, preferably a mixed solvent of water and ethanol, a mixed solvent of ethanol and isopropanol, and more preferably a mixed solvent of ethanol and isopropanol.

[0049] In one embodiment of the present invention, solvent II is composed of water and a low-carbon alcohol solvent, and the volume ratio of water to low-carbon alcohol solvent is 5~7:3~5, for example, it can be 5:3, 5:4, 1:1, 2:1, 3:2, 6:5, 13:7, 7:5, preferably 3:2. When the volume ratio of water to low-carbon alcohol solvent is 3:2, its evaporation rate and dispersion stability of each component of the coating slurry are optimal.

[0050] In this invention, the preparation method of solvent II includes the following steps: Water is purified by reverse osmosis to remove impurities, ions, and microorganisms, resulting in treated water. The low-carbon alcohol solvent is dehydrated to control the moisture content to ≤0.5%, thus obtaining the treated low-carbon alcohol solvent. The treated water and the treated low-carbon alcohol solvent were mixed and stirred at 400-600 r / min for 20-25 min, then allowed to stand for 15-20 min to remove bubbles, thus obtaining solvent II.

[0051] In this invention, porous ceramic powder and dispersant are added to solvent II. During dispersion, the dispersion is carried out at a rotation speed of 1800~2200 r / min for 35~45 min. The rotation speed can be any value or any range between two values ​​from 1800 r / min, 1900 r / min, 2000 r / min, 2100 r / min, and 2200 r / min. The dispersion time can be any value or any range between two values ​​from 35 min, 40 min, and 45 min.

[0052] In this invention, during the preparation of the coating slurry, the coating slurry containing porous ceramic powder, dispersant, fully aromatic multi-component copolymer polyacrylate resin, photoinitiator, and leveling agent is milled during blending to obtain D. 50 ≤200nm, solid content 30%~55%, viscosity 100~800mPa s coating s.

[0053] In this invention, the coating slurry is applied to the base film, and during curing, it is cured under nitrogen protection using an ultraviolet light source with an ultraviolet energy of 800~1500 mJ / cm². 2 Within this ultraviolet energy range, in-situ crosslinking and curing of the base film coated with the coating slurry can achieve rapid forming of composite coatings. When the ultraviolet energy is <800mJ / cm 2 At times, insufficient cross-linking and curing of the coating may occur, especially when the UV energy is >1500 mJ / cm. 2 In a short period of time, excessive cross-linking of the coating may occur, which may cause internal stress between the composite coating and the base film surface, which is not conducive to improving the overall stability of the lithium battery separator.

[0054] In this invention, after the composite coating is cured, the solvent is removed by a segmented low-temperature drying method of 60℃→80℃→100℃. First, it is dried at 60℃ for 3 minutes, then the temperature is raised to 80℃ and dried for 2 minutes, and then the temperature is raised to 100℃ and dried for 2 minutes.

[0055] In one embodiment of the present invention, the thickness of the composite coating on one side is 1~5μm.

[0056] In this invention, a coating slurry is applied to a base film, and the thickness of the composite coating on one side is controlled to be 1~5μm. For example, it can be any point value or any range between any two points from 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, to 5μm. By controlling the thickness of the composite coating to 1~5μm, the ion transport effect of the composite coating after curing and the maintenance of the mechanical integrity of the separator can be balanced, thereby improving the overall structural stability and ionic conductivity of the final lithium battery separator. When the thickness of the composite coating is <1μm, the separator is prone to uneven thickness, which will also result in insufficient heat resistance and mechanical strength. When the thickness of the composite coating is >5μm, the composite coating is relatively thick, which will lead to a decrease in the overall flexibility of the lithium battery separator, resulting in cracking and peeling during winding or bending. At the same time, an excessively thick composite separator is not conducive to improving ionic conductivity, thus affecting the overall performance of the lithium battery separator.

[0057] A specific embodiment of the third aspect of the present invention provides a battery, including a photocurable composite lithium battery separator provided in the specific embodiment of the first aspect of the present invention or a photocurable composite lithium battery separator prepared by the preparation method provided in the specific embodiment of the second aspect of the present invention.

[0058] The present invention will now be described in detail with reference to preferred embodiments and comparative examples. The preferred embodiments of the present invention described below can be modified in various ways, and therefore the scope of the invention should not be construed as limited to the preferred embodiments described in detail below. Preferred embodiments are provided to help those skilled in the art to more readily understand the present invention.

[0059] Detailed information on some of the components used in the following examples and comparative examples is as follows: Porous alumina I: pore size distribution is 2~20nm, specific surface area is 150m² 2 / g, pore volume 0.55cm 3 / g; Porous alumina II: pore size distribution is 10~50 nm, specific surface area is 180 m². 2 / g, pore volume 0.60cm 3 / g; Porous alumina III: pore size distribution of 2~50 nm, specific surface area of ​​160 m² 2 / g, pore volume 0.58cm 3 / g; Nano-alumina: Specific surface area of ​​120m² 2 / g; Polyacrylate dispersant: Model BYK-P104; Ammonium carboxylate dispersant: Model TAMOL 1222; Phosphate ester dispersant: Model BYK-110; Polyether-modified silicone leveling agent: model number BYK-333; Acrylic leveling agent: Model BYK-358; The preparation method of the mixed solvent in the coating slurry preparation process is as follows: A1. Deionized water is purified by reverse osmosis to remove impurity ions and microorganisms, resulting in treated deionized water. A2. The low-carbon alcohol solvent is dehydrated to control the moisture content to 0.3% to obtain the treated low-carbon alcohol solvent; A3. Mix the treated deionized water and the treated low-carbon alcohol solvent, stir at 500 r / min for 25 min, let stand for 15 min to remove bubbles, and obtain the mixed solvent.

[0060] Example 1 A method for preparing a photocurable composite lithium battery separator includes the following steps: S0. Add 200 parts of a 1:1 volume ratio mixture of cyclohexanone and propylene glycol methyl ether acetate to a reactor equipped with a mechanical stirrer, reflux condenser, nitrogen inlet pipe, and constant pressure dropping funnel. Start stirring and continuously purge with nitrogen for 30 minutes. Heat the reactor to 85°C and maintain a constant temperature. Blend 60 parts of bisphenol A dimethacrylate, 15 parts of N-phenylmaleimide, 20 parts of isocyanate methacrylate, and 5 parts of trimethylolpropane triacrylate, stirring until fully combined. The mixture was completely dissolved and homogeneous, yielding a mixed monomer solution. 1.5% (by weight of the total functional monomers) of azobisisoheptanenitrile was added to this mixed monomer solution, and the mixture was stirred until completely dissolved to obtain a mixed liquid. The mixed liquid was transferred to a constant-pressure dropping funnel and, under nitrogen protection at 85°C, was dropped into a reaction vessel over a period of 3.5 hours. After the addition was complete, the reaction was maintained at 85°C for 6 hours, cooled, and distilled under reduced pressure to obtain a fully aromatic multi-component copolymer polyacrylate resin (Tg = 295°C), which was then sealed and stored away from light. S1. Add 75 parts of porous alumina I and 1.2 parts of polyacrylate dispersant to a mixed solvent of deionized water and ethanol at a volume ratio of 3:2. Disperse at 2000 r / min for 40 min. Then, add 22 parts of fully aromatic multi-component copolyacrylate resin (Tg=295℃), 1.5 parts of photoinitiator TPO, and 0.3 parts of polyether-modified silicone leveling agent in sequence. Continue stirring for 30 min, then transfer to a sand mill to obtain the coating slurry (D of the coating slurry). 50 (180 nm, solid content 48%, viscosity 420 mPa·s). S2. Apply the above coating slurry to one side of a 7μm thick polyethylene film, controlling the coating thickness to be 2μm, and apply it under nitrogen protection at 1400mJ / cm². 2 The film is cured by ultraviolet energy, then dried at 60°C for 3 minutes, heated to 80°C and dried for 2 minutes, and then heated to 100°C and dried for 2 minutes to obtain a photocured composite lithium battery separator.

[0061] Example 2 A method for preparing a photocurable composite lithium battery separator includes the following steps: S0. Add 200 parts of a mixed solution of methyl isobutyl ketone and cyclohexanone (3:2 volume ratio) to a reactor equipped with a mechanical stirrer, reflux condenser, nitrogen inlet pipe, and constant pressure dropping funnel. Start stirring and continuously purge with nitrogen for 30 minutes. Heat the reactor to 80°C and maintain a constant temperature. Blend 55 parts of 9,9-diphenylfluorene methacrylate, 20 parts of styrene, 15 parts of N-cyclohexylmaleimide, and 10 parts of neopentyl glycol diacrylate functional monomers together and stir until completely blended. The solution was dissolved and homogeneous, yielding a mixed monomer solution. 1.2% (by weight of the total functional monomers) of azobisisobutyronitrile (AIBN) was added to this mixed monomer solution and stirred until completely dissolved, yielding a mixed liquid. The mixed liquid was transferred to a constant-pressure dropping funnel and, under nitrogen protection at 80°C, was dropped into a reaction vessel over a period of 3 hours. After the addition was complete, the reaction was maintained at 80°C for 5 hours, cooled, and distilled under reduced pressure to obtain a fully aromatic multi-component copolymer polyacrylate resin (Tg = 282°C), which was then sealed and stored away from light. S1. Add 80 parts of porous alumina II and 1.0 part of phosphate ester dispersant to a mixed solvent of deionized water and isopropanol with a volume ratio of 13:7. After dispersing at 2000 r / min for 45 min, add 17 parts of fully aromatic multi-component copolyacrylate resin (Tg=282℃), 1.2 parts of photoinitiator 184, and 0.3 parts of acrylate leveling agent in sequence. Continue stirring for 35 min, then transfer to a sand mill for sand milling to obtain the coating slurry (D of the coating slurry). 50 (180 nm, solid content 48%, viscosity 420 mPa·s). S2. Apply the above coating slurry to both sides of a 7μm thick polyethylene film, controlling the coating thickness on one side to be 3μm. Then, under nitrogen protection, apply 1300mJ / cm² of the coating. 2 The film is cured by ultraviolet energy, then dried at 60°C for 3 minutes, heated to 80°C and dried for 2 minutes, and then heated to 100°C and dried for 2 minutes to obtain a photocured composite lithium battery separator.

[0062] Example 3 A method for preparing a photocurable composite lithium battery separator includes the following steps: S1. Add 82 parts of porous alumina III and 1.5 parts of polyacrylate dispersant to a mixed solvent of deionized water and isopropanol with a volume ratio of 3:2. Disperse at 2200 r / min for 35 min. Then, add 15 parts of fully aromatic multi-component copolyacrylate resin (Tg=282℃), 0.5 parts of photoinitiator 184, 0.5 parts of photoinitiator TPO, and 0.2 parts of polyether-modified silicone leveling agent in sequence. Continue stirring for 30 min, then transfer to a sand mill for sand milling to obtain the coating slurry (D of the coating slurry). 50 (200 nm, solid content 52%, viscosity 600 mPa·s). S2. Apply the above coating slurry to one side of a 7μm thick polyethylene film, controlling the coating thickness to be 1.5μm, and apply it under nitrogen protection at 1000mJ / cm. 2 The UV energy is used to cure the film, and then it is dried at 60℃ for 3 minutes, then heated to 80℃ and dried for 2 minutes, and then heated to 100℃ and dried for 2 minutes to obtain a photocurable composite lithium battery separator. The preparation method of the fully aromatic multi-component copolyacrylate resin (Tg=282℃) is the same as step S0 in Example 2.

[0063] Example 4 A method for preparing a photocurable composite lithium battery separator includes the following steps: S1. Add 70 parts of porous alumina I and 0.8 parts of ammonium carboxylate dispersant to a mixed solvent of deionized water and ethanol at a volume ratio of 11:9. After dispersing at 1800 r / min for 40 min, add 25 parts of fully aromatic multi-component copolyacrylate resin (Tg=295℃), 1.8 parts of photoinitiator 819, and 0.2 parts of polyether-modified silicone leveling agent in sequence. Continue stirring for 30 min, then transfer to a sand mill to obtain the coating slurry (D of the coating slurry). 50 (170 nm, solid content 40%, viscosity 280 mPa·s). S2. Apply the above coating slurry to one side of a 7μm thick polyethylene film, controlling the coating thickness to be 2.5μm, and apply it under nitrogen protection at 1400mJ / cm. 2 The UV energy is used to cure the film, and then it is dried at 60℃ for 3 minutes, then heated to 80℃ and dried for 2 minutes, and then heated to 100℃ and dried for 2 minutes to obtain a photocurable composite lithium battery separator. The preparation method of the fully aromatic multi-component copolyacrylate resin (Tg=295℃) is the same as step S0 in Example 1.

[0064] Example 5 A method for preparing a photocurable composite lithium battery separator includes the following steps: S1. Add 78 parts of porous alumina II and 1.5 parts of polyacrylate dispersant to a mixed solvent of deionized water, ethanol and isopropanol in a volume ratio of 3:1:1. Disperse at 2200 r / min for 35 min. Then, add 20 parts of fully aromatic multi-component copolyacrylate resin (Tg=282℃), 1.2 parts of photoinitiator TPO and 0.4 parts of acrylate leveling agent in sequence. Continue stirring for 30 min, then transfer to a sand mill for sand milling to obtain the coating slurry (D of the coating slurry). 50 (190 nm, solid content 38%, viscosity 320 mPa·s). S2. Apply the above coating slurry to one side of a 7μm thick polyethylene film, controlling the coating thickness to be 2.0μm, and apply it under nitrogen protection at 1100mJ / cm². 2 The UV energy is used to cure the film, and then it is dried at 60℃ for 3 minutes, then heated to 80℃ and dried for 2 minutes, and then heated to 100℃ and dried for 2 minutes to obtain a photocurable composite lithium battery separator. The preparation method of the fully aromatic multi-component copolyacrylate resin (Tg=282℃) is the same as step S0 in Example 2.

[0065] Example 6 This embodiment is the same as Example 1, except that 60 parts of bisphenol A dimethacrylate and 15 parts of N-phenylmaleimide are replaced with an equal amount of methyl methacrylate.

[0066] Example 7 This embodiment is the same as Example 1, except that 15 parts of N-phenylmaleimide are replaced with an equal amount of butyl acrylate.

[0067] Example 8 This embodiment is the same as Example 1, except that 20 parts of isocyanate methacrylate are replaced with an equal amount of styrene.

[0068] Example 9 This embodiment is identical to Example 1 except that 60 parts of bisphenol A dimethacrylate are replaced with an equal amount of methyl methacrylate and 15 parts of N-phenylmaleimide are replaced with an equal amount of butyl acrylate.

[0069] Example 10 This embodiment is the same as Example 1, except that porous alumina is replaced with an equal amount of nano alumina.

[0070] Example 11 This embodiment is the same as Example 1, except that the coating thickness is controlled to 6μm.

[0071] Example 12 This embodiment reduces the UV curing energy to 500 mJ / cm². 2 Except for the above, the rest is the same as in Example 1.

[0072] Example 13 This embodiment is the same as Example 1 except that ethanol is replaced with deionized water.

[0073] Comparative Example 1 This comparative example is the same as Example 1 except that the fully aromatic multi-component copolymer polyacrylate resin (Tg=295℃) is replaced with an equal amount of thermosetting acrylate resin (Tg=61℃) and the UV curing is replaced with 80℃ hot air baking curing. The preparation method of thermosetting acrylic resin (Tg=61℃) includes the following steps: Add 200 parts of butyl acetate to the reactor, start stirring and continuously purge with nitrogen for 30 minutes, heat the reactor to 70℃ and maintain a constant temperature; mix 40 parts of methyl methacrylate and 60 parts of butyl acrylate functional monomers evenly, add 1.0% of azobisisobutyronitrile by mass of the total functional monomers, stir to dissolve, and obtain a mixture; under nitrogen protection at 70℃, dropwise add the mixture into the reactor over a period of 2 hours; after the addition is complete, keep the reaction at 70℃ for 6 hours, cool, and distill under reduced pressure to obtain a thermosetting acrylate resin (Tg=61℃), which is then sealed and stored away from light.

[0074] Comparative Example 2 This comparative example is the same as Example 1 except that the fully aromatic multi-component copolyacrylate resin (Tg=295℃) is replaced with an equal amount of soft acrylate (Tg=53℃). The preparation method of soft acrylic resin (Tg=53℃) includes the following steps: Add 200 parts of butyl acetate to the reactor, start stirring and continuously purge with nitrogen for 30 minutes. Heat the reactor to 70°C and maintain the temperature. Add 100 parts of isooctyl acrylate and 1 part of azobisisobutyronitrile to the reactor and stir until homogeneous. Under nitrogen protection at 70°C, keep the reaction at this temperature for 6 hours. Cool and distill under reduced pressure to obtain soft acrylate resin (Tg=50°C). Store in a sealed container away from light.

[0075] The following performance tests were performed on the lithium battery separators of Examples 1-13 and Comparative Examples 1-2: (1) Thickness: The thickness of the lithium battery separator was tested according to the method in GB / T 36363-2018 "Polyolefin separator for lithium-ion batteries"; (2) Air permeability: The air permeability of the lithium battery separator was tested according to the method in GB / T 36363-2018 "Polyolefin separator for lithium-ion batteries"; (3) Areal density: The areal density of the lithium battery separator was tested according to the method in GB / T 36363-2018 "Polyolefin separator for lithium-ion batteries"; (4) Heat shrinkage rate: The transverse (TD) and longitudinal (MD) heat shrinkage rates at 150℃ were determined according to the test method in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries". The separator sample size was 100mm×100mm, and the test results of transverse and longitudinal heat shrinkage rates were the average values ​​of 3 samples. (5) Static contact angle: The static contact angle of the electrolyte was tested according to the test method in GB / T 30693-2014 "Measurement of contact angle between plastic film and water". The electrolyte was a mixture of electrolyte and solvent. The electrolyte was lithium hexafluorophosphate and the solvent was a mixture of ethylene carbonate and diethyl carbonate (the volume ratio of ethylene carbonate and diethyl carbonate was 1:1). The concentration of electrolyte in the electrolyte was 1 mol / L. (6) Ionic conductivity: The ionic conductivity was tested according to the method in GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries", where the temperature was 40℃ and the relative humidity was 50%. (7) Liquid absorption rate and liquid retention rate: Cut the diaphragm into 50mm×50mm samples, and weigh the samples before testing and record the weight as m1; Liquid absorption rate test procedure: Immerse the weighed diaphragm in the electrolyte at 25℃ for 30 minutes, remove it, place it on industrial wiping paper, wipe off the free electrolyte with industrial wiping paper, and weigh it as m2; Liquid retention rate test procedure: After the liquid absorption rate is weighed, place the sample at 25℃ for 1 hour and record it as m3. Liquid absorption rate (%) = (m2-m1) / m1×100; Liquid retention rate (%) = (m3-m1) / m1×100; The electrolyte used is the same as that used in the static contact angle test. (8) Liquid creep rate: Cut the diaphragm sample into strips of 20mm×100mm and let them stand at 25℃ and 50% relative humidity to reach equilibrium. At the same time, let the electrolyte stand (the electrolyte is the same as the electrolyte in the static contact angle test). The vertical suspension method was used, and the lower end of the diaphragm sample was vertically immersed in the electrolyte for 5 mm, keeping the diaphragm sample vertical without bending or wrinkles; the time was started from the immersion time, and the height h (unit: mm) of the electrolyte climbing up the diaphragm sample was recorded after 10 min; the climbing rate was calculated according to the formula: climbing rate (mm / min) = climbing height h / test time t; the test results are all average values ​​of 3 samples.

[0076] The test results are shown in Table 1: Table 1 Performance test results of Examples 1-13 and Comparative Examples 1-2

[0077] As can be seen from Table 1, compared with Comparative Examples 1-2, the lithium battery separators prepared in Examples 1-5 showed significantly lower lateral and longitudinal thermal shrinkage rates at 150°C. This indicates that the addition of a fully aromatic multi-component copolymer polyacrylate resin with a glass transition temperature of 270-300°C to the composite coating, under the action of a photoinitiator and after cross-linking and curing, can solve the problems of conventional adhesives being prone to softening and having poor thermal shrinkage performance at high temperatures. At the same time, the fully aromatic multi-component copolymer polyacrylate resin forms a uniform film in the composite coating, which can effectively preserve the pore structure of the ceramic powder, thereby effectively improving the heat resistance and ionic conductivity of the lithium battery separator.

[0078] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photocurable composite lithium battery separator, characterized in that, Includes a base film and a composite coating disposed on at least one surface of the base film; The raw materials for the composite coating include porous ceramic powder, fully aromatic multi-component copolyacrylate resin, and photoinitiator; The glass transition temperature of the fully aromatic multi-component copolymer polyacrylate resin is 270~300℃.

2. The photocurable composite lithium battery separator according to claim 1, characterized in that, The mass ratio of the porous ceramic powder to the fully aromatic multi-component copolyacrylate resin is 50~85:12~40; The porous ceramic powder has a pore size distribution of 2~50nm and a specific surface area of ​​80~200m². 2 / g.

3. The photocurable composite lithium battery separator according to claim 1, characterized in that, The raw materials for the fully aromatic multi-component copolyacrylate resin include functional monomers and initiators in a weight ratio of 100:1.2~1.

5.

4. The photocurable composite lithium battery separator according to claim 3, characterized in that, The functional monomers are functional monomer I, functional monomer II, functional monomer III, and functional monomer IV; The functional monomer I includes one or more of bisphenol A dimethacrylate, bisphenol S dimethacrylate, and biphenyl dimethacrylate; The functional monomer II includes one or both of N-phenylmaleimide and N-benzylmaleimide; The functional monomer III includes one or more of the following: isocyanate-containing functional monomers, hydroxyl-containing functional monomers, and epoxy-containing functional monomers. The functional monomer IV includes one or more of trimethylolpropane triacrylate, pentaerythritol tetraacrylate, and ethoxylated trimethylolpropane triacrylate.

5. The photocurable composite lithium battery separator according to claim 3, characterized in that, The functional monomers are functional monomer I, functional monomer II, and functional monomer IV; The functional monomer I includes one or more of 9,9-diphenylfluorenyl methacrylate, styrene, and methylstyrene; The functional monomer II includes one or both of N-cyclohexylmaleimide and N-phenylmaleimide; The functional monomer IV includes one or both of neopentyl glycol diacrylate and 1,6-hexanediol diacrylate.

6. The photocurable composite lithium battery separator according to claim 3, characterized in that, The preparation method of the fully aromatic multi-component copolyacrylate resin includes the following steps: The functional monomer and initiator are blended and added to solvent I for reaction to obtain the fully aromatic multi-component copolyacrylate resin.

7. The photocurable composite lithium battery separator according to claim 1, characterized in that, The thickness of the composite coating on one side is 1~5μm.

8. The photocurable composite lithium battery separator according to claim 1, characterized in that, The raw materials for the composite coating also include dispersants and leveling agents; The weight ratio of the porous ceramic powder, the fully aromatic multi-component copolymer polyacrylate resin, the photoinitiator, the dispersant, and the leveling agent is 50~85:12~40:0.5~3:0.3~2:0.1~1.

9. A method for preparing a photocurable composite lithium battery separator, used to prepare a photocurable composite lithium battery separator as described in any one of claims 1 to 8, characterized in that, Includes the following steps: The raw materials for the composite coating are mixed to obtain a coating slurry; The coating slurry is coated on one or both sides of the base film, cured, and dried to obtain the photocurable composite lithium battery separator.

10. A battery, characterized in that, Includes a photocurable composite lithium battery separator as described in any one of claims 1 to 8, or a photocurable composite lithium battery separator prepared by the preparation method described in claim 9.

Images