A binder for a fire-retardant ceramic-coated separator and a method for preparing the same

Abstract

The application discloses a kind of binder for fire-retardant ceramic-coated diaphragm and preparation method thereof, belong to binder technical field;The active ingredient of the binder is phosphonated polyphenyl ether, which is prepared by introducing at least one phosphorus-containing functional group selected from phosphonic acid group, phosphate group and phosphate group on the main chain and / or side chain of polyphenyl ether;Preparation method includes: poly (2,6-dimethyl-1,4-phenyl ether) is brominated to obtain brominated polyphenyl ether through side chain, and then phosphate group-containing phosphonated polyphenyl ether is prepared through phosphate synthesis reaction;The binder has excellent flame retardancy, super-strong inorganic bonding force, high electrolyte affinity and good thermal stability, and when applied to lithium ion battery diaphragm ceramic coating, can significantly improve the safety performance, structural stability and electrochemical performance of the battery, solve the technical problems of existing binder, such as insufficient flame retardancy, weak bonding force and poor electrolyte wettability.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to an adhesive for flame-retardant ceramic-coated diaphragms and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, new energy vehicles, and energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. The separator, as one of the core components of a lithium-ion battery, primarily functions to separate the positive and negative electrodes, prevent short circuits, and allow lithium ions to pass freely. Its performance directly affects the battery's safety, cycle life, and rate performance.

[0003] Currently, commercial lithium-ion battery separators mostly use polyolefin (polyethylene PE, polypropylene PP) base films, but their thermal stability is poor, and they are prone to thermal shrinkage above 120℃, which may lead to internal short circuits and thermal runaway. To solve this problem, the industry generally adopts the method of coating the surface of polyolefin base films with inorganic ceramic particles (such as alumina, boehmite, zirconium oxide, etc.) to prepare ceramic-coated separators, thereby improving the thermal stability and mechanical strength of the separator. As a key component of the ceramic coating, the binder must firmly bond the ceramic particles to the surface of the base film and ensure good compatibility between the coating and the electrolyte. Its performance directly determines the overall quality of the ceramic-coated separator.

[0004] The binders commonly used in existing ceramic-coated separators mainly include organic polymers such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC). However, these traditional organic binders are flammable. When the battery experiences thermal runaway, the ceramic coating will burn or fall off along with the binder, failing to form effective protection. This causes the separator to lose its isolation function, exacerbating the risk of battery fire and explosion, and making it difficult to meet high-end flame retardant standards such as UL94V-0. At the same time, most traditional binders have weak polarity and insufficient affinity for non-aqueous electrolytes (such as carbonate mixed solvents containing LiPF6), resulting in long electrolyte wetting time and low ionic conductivity after battery assembly, which in turn affects the battery's initial discharge capacity and high-rate performance. Moreover, binders such as SBR and CMC have low glass transition temperatures and are prone to softening and decomposition under high-temperature conditions, causing the ceramic coating structure to collapse and failing to guarantee the dimensional stability of the separator.

[0005] To address these issues, existing technologies attempt to modify existing adhesives (such as grafting polar groups onto PVDF) or develop new adhesives. However, these modifications often involve complex processes, high costs, and limited performance characteristics, making it difficult to achieve a comprehensive improvement in flame retardancy, adhesion, electrolyte wetting, and thermal stability. Summary of the Invention

[0006] The present invention aims to solve the combined problems of poor flame retardancy, insufficient adhesion, and poor electrolyte wettability of existing adhesives for flame-retardant ceramic coated diaphragms.

[0007] To address the above problems, the present invention provides an adhesive for flame-retardant ceramic-coated diaphragms, wherein the active ingredient of the adhesive is phosphorylated polyphenylene ether (P-PPO), and the phosphorylated polyphenylene ether is a functional polymer obtained by introducing phosphorus-containing functional groups into the main chain and / or side chain of polyphenylene ether (PPO).

[0008] The flame-retardant ceramic-coated diaphragm adhesive of the present invention has, but is not limited to, the following beneficial effects compared with the prior art: The adhesive for flame-retardant ceramic coated separators of this invention introduces phosphorus-containing functional groups. When the battery experiences thermal runaway, the phosphorus-containing functional groups decompose to form non-volatile phosphoric acid, which promotes carbonization of the polymer and ceramic particle surfaces, forming a dense, heat-insulating carbon layer. This effectively blocks the transfer of oxygen and heat, enabling the coated separator to meet the UL94V-0 standard or higher for high flame retardancy. This completely changes the current situation where traditional PVDF, SBR, and other adhesives are inherently flammable and the coating is prone to burning and peeling off, thus significantly improving battery safety performance.

[0009] Meanwhile, the phosphorus-containing functional groups (especially phosphate groups) in phosphorylated polyphenylene ether can form strong hydrogen bonds or coordination bonds with the hydroxyl groups (-OH) remaining on the surface of ceramic particles (such as Al2O3), achieving chemical anchoring. Compared with the physical adsorption of existing binders such as polyvinylidene fluoride (PVDF), the adhesion strength between the coating and the particles is significantly improved, which can effectively avoid the coating peeling problem under long-term cycling or high-temperature environment and eliminate the risk of short circuit in the battery.

[0010] Moreover, phosphorus-containing functional groups (phosphate / phosphate ester groups) are highly polar groups, which can significantly enhance the affinity between the flame-retardant ceramic coating and the non-aqueous electrolyte, shorten the electrolyte wetting time, and thus improve the battery's first discharge capacity and rate performance. This solves the problem of slow electrolyte wetting and low ionic conductivity caused by the lack of polar groups in existing binders. The PPO main skeleton has a high glass transition temperature. As the core skeleton of the active ingredient, it can ensure that the binder can maintain dimensional stability and mechanical strength in high-temperature environments above 150°C, avoid membrane shrinkage or damage, and meet the high-temperature operating requirements of lithium-ion batteries.

[0011] Preferably, the phosphorus-containing functional group is at least one of a phosphate group (-PO(OH)2), a phosphate ester group (-PO(OR)2), or a phosphate group (-PO(OM)2).

[0012] Specifically, -PO(OH)2 has the strongest polarity, exhibiting the best adhesion to ceramic particles and electrolyte wettability, making it suitable for scenarios with extremely high requirements for bonding strength and rate performance; -PO(OR)2 has an easy-to-control synthesis process and good product compatibility, making it suitable for large-scale industrial production; -PO(OM)2 has higher flame retardant efficiency, meeting the needs of high-safety-level batteries; selecting single or combined functional groups according to the actual application scenario can solve the problem of existing single-functional group binders having limited performance and being unable to meet the needs of multiple scenarios.

[0013] The present invention also provides a preparation method for preparing the adhesive for flame-retardant ceramic-coated diaphragms as described above, comprising the following steps: Step 1: Dissolve poly(2,6-dimethyl-1,4-phenyl ether) in a high-boiling-point solvent, add N-bromosuccinimide (NBS) and an initiator, and carry out a side-chain bromination reaction at 90-130℃ to obtain the reaction product; add alcohol to the reaction product for precipitation washing and drying to obtain brominated polyphenyl ether; Step 2: Dissolve the brominated polyphenylene ether in an aprotic solvent, and add triethyl phosphite (P(OEt)3), wherein the amount of triethyl phosphite added is 1.2-3.0 times the molar amount of the brominated polyphenylene ether; carry out the phosphate ester synthesis reaction (Michaelis–Arbuzov) at 120-160℃ to obtain the reaction product; add a non-solvent to the reaction product for precipitation washing and drying to obtain phosphorylated polyphenylene ether containing phosphate ester groups.

[0014] The method for preparing the adhesive for flame-retardant ceramic-coated diaphragms of the present invention has, but is not limited to, the following beneficial effects compared with the prior art: In step 1, NBS, as a brominating agent, works synergistically with the initiator to achieve precise bromination of PPO side chains under reflux conditions of 90-130℃, while avoiding side reactions such as main chain breakage. The high-boiling-point solvent provides a good dissolution environment for PPO, ensuring the uniformity of the reaction system. The precipitation, washing, and drying steps effectively remove unreacted raw materials and impurities, thereby improving the purity of brominated polyphenylene ether and solving the problems of low product purity and unstable bromination rate in existing bromination processes.

[0015] In step 2, the amount of P(OEt)3 is set to 1.2-3.0 times the molar amount of brominated polyphenylene ether. This ratio ensures complete conversion of brominated polyphenylene ether (avoiding residual brominated groups from affecting product performance) without causing waste of raw materials and increased difficulty in post-processing due to excessive amount. The reaction temperature of 120-160℃ is suitable for Michaelis-Arbuzov's kinetic requirements, and the reaction rate and product selectivity are in balance.

[0016] Moreover, the entire preparation process only includes three core steps: bromination, phosphorylation, and precipitation purification. It does not require complex equipment, the reaction conditions are mild, and precipitation, washing, and drying are routine operations, making it easy to scale up production. PPO, NBS, and P(OEt)3 are readily available and have stable prices. The reaction process does not produce any toxic or harmful gases, the post-processing steps are simple, the environmental pressure is low, and it meets the requirements of green production.

[0017] Preferred options also include: Step 3: Add the phosphorylated polyphenylene ether containing phosphate ester groups to concentrated hydrochloric acid or hydrogen bromide solution and heat to hydrolyze. Neutralize the hydrolysate with alkaline solution to pH=6-7, filter, wash and dry to obtain phosphorylated polyphenylene ether containing phosphate groups.

[0018] Specifically, by heating and hydrolyzing with concentrated hydrochloric acid or hydrogen bromide solution, -PO(OR)2 can be converted into -PO(OH)2. The hydroxyl groups (-OH) of the phosphate group can form stronger hydrogen bonds and coordination bonds with the hydroxyl groups on the surface of ceramic particles. Compared with phosphate ester groups, the bonding strength and electrolyte wettability are improved, which can meet the requirements of scenarios with higher bonding strength and rate performance. Moreover, the hydrolysis reaction only requires the addition of concentrated hydrochloric acid or hydrogen bromide solution and heating, without the need for additional catalysts. The reaction conditions are mild, and the post-treatment only requires conventional neutralization, precipitation and washing, without the need for complex separation equipment. This can solve the contradiction between easy synthesis and high performance that existing binders cannot achieve.

[0019] Preferably, in step 1, the high-boiling-point solvent is chlorobenzene.

[0020] Specifically, chlorobenzene exhibits excellent solubility for poly(2,6-dimethyl-1,4-phenylene ether), enabling complete dissolution of poly(2,6-dimethyl-1,4-phenylene ether) to form a homogeneous solution. This avoids incomplete bromination due to localized undissolved areas, ensuring a stable bromination rate. Simultaneously, chlorobenzene demonstrates good solubility for NBS and the initiator, forming a homogeneous reaction system with uniform reaction rates.

[0021] Preferably, in step 1, the molar ratio of poly(2,6-dimethyl-1,4-phenyl ether) to N-bromosuccinimide is 1:(0.3-0.8).

[0022] Specifically, with a molar ratio of 1:(0.3-0.8), the methyl groups on the side chains of poly(2,6-dimethyl-1,4-phenyl ether) can achieve a bromination rate of 30%-80%. This ensures sufficient active sites for subsequent phosphorylation reactions, guarantees the grafting density of phosphorus-containing functional groups, and prevents degradation of the poly(2,6-dimethyl-1,4-phenyl ether) main chain (such as chain breaking or cross-linking) due to excessive bromination rate, or insufficient product performance due to excessively low bromination rate.

[0023] Preferably, in step 1, the initiator is benzoyl peroxide, and the amount of benzoyl peroxide (BPO) added is 0.5-2 wt% of the sum of the mass of poly(2,6-dimethyl-1,4-phenyl ether) and N-bromosuccinimide.

[0024] Specifically, BPO is a free radical initiator that can rapidly decompose to generate free radicals at 90-130℃, precisely initiating the bromination reaction of NBS with the methyl side chain of poly(2,6-dimethyl-1,4-phenylene ether). It has high initiation efficiency and is more suitable for the reaction temperature requirements of high-boiling-point solvent systems compared to other initiators (such as azobisisobutyronitrile). The amount of BPO added ensures a sufficient concentration of free radicals, allowing the bromination reaction to proceed continuously and efficiently, while avoiding the polymerization of free radicals due to excessive initiator, which could lead to side reactions such as main chain crosslinking and chain scission.

[0025] Preferably, in step 2, the aprotic solvent is at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0026] Specifically, DMF, NMP, and DMSO all have good solubility for brominated polyphenylene ethers and P(OEt)3, which can form a homogeneous reaction system, avoiding incomplete local reactions caused by insufficient dissolution of raw materials, and ensuring that the phosphoric acid esterification reaction proceeds uniformly.

[0027] Preferably, in step 3, if a concentrated hydrochloric acid solution is used, the mass fraction of hydrochloric acid in the concentrated hydrochloric acid solution is 36-38%; if a hydrogen bromide solution is used, the mass fraction of hydrogen bromide in the hydrogen bromide solution is 40-48%.

[0028] Specifically, when the mass fraction of concentrated hydrochloric acid is 36-38% and the mass fraction of hydrogen bromide solution is 40-48%, there is a sufficient proton concentration to quickly break the CO bond of the phosphate ester group, thereby increasing the hydrolysis rate. Furthermore, the concentration will not lead to degradation of the PPO main chain (such as main chain breakage or cross-linking) due to excessively high concentration, or incomplete hydrolysis due to excessively low concentration.

[0029] Preferably, in step 1, the bromination reaction takes 2-10 hours; in step 2, the phosphate ester synthesis reaction takes 4-12 hours.

[0030] Specifically, the bromination reaction time in step 1 is 2-10 hours. This time is such that the bromination is incomplete due to the short time, and the side reactions increase due to the long time. The phosphate ester synthesis reaction time in step 2 is 4-12 hours. This ensures the complete conversion of brominated polyphenylene ether and avoids the product having residual brominated groups due to the short time, or the phosphate ester groups being hydrolyzed or decomposed due to the long time. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0032] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0034] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0035] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0036] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this application can be purchased commercially or prepared by existing methods. For example, the sources and types of raw materials involved in the following examples and comparative examples are as follows: Poly(2,6-dimethyl-1,4-phenylene ether) (PPO): Model PPO 640Z, number average molecular weight 50000 g / mol, purchased from Sabic, USA; N-bromosuccinimide (NBS): Analytical grade, ≥99.0%, purchased from Aladdin Reagent (Shanghai) Co., Ltd. Benzoyl peroxide (BPO): analytical grade, purity ≥98.0%, purchased from Sigma-Aldrich (USA); Chlorobenzene: analytical grade, ≥99.5%, purchased from Sinopharm Chemical Reagent Co., Ltd. Anhydrous ethanol: analytical grade, ≥99.7%, purchased from Sinopharm Chemical Reagent Co., Ltd.; N,N-Dimethylformamide (DMF): Analytical grade, ≥99.5%, purchased from Aladdin Reagent (Shanghai) Co., Ltd.; Triethyl phosphite (P(OEt)3): analytical grade, ≥98.0%, purchased from Aladdin Reagent (Shanghai) Co., Ltd. Concentrated hydrochloric acid: industrial grade, purchased from Sinopharm Chemical Reagent Co., Ltd.; Hydrogen bromide solution: industrial grade, purchased from Aladdin Reagent (Shanghai) Co., Ltd.; Sodium hydroxide: analytical grade, ≥96.0%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Sodium bicarbonate: analytical grade, ≥99.0%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Petroleum ether: analytical grade, ≥99.0%, purchased from Sinopharm Chemical Reagent Co., Ltd.; Aluminum oxide (Al2O3) particles: spherical α-Al2O3, average particle size 1.0μm, purity ≥99.9%, purchased from Shandong Dongjia Group Co., Ltd. Polyethylene glycol: PEG2000, analytical grade, purchased from Aladdin Reagent (Shanghai) Co., Ltd.; Polyethylene (PE) base film: Single-layer PE film, 12µm thick, 40% porosity, purchased from Shenzhen Xingyuan Material Technology Co., Ltd. Polyvinylidene fluoride (PVDF): PVDF1100, industrial grade, purchased from Shanghai Sanai New Materials Co., Ltd. Styrene-butadiene rubber (SBR): SBR1502 (emulsion type, solid content 40%), industrial grade, purchased from Beijing Yanshan Branch of China Petroleum & Chemical Corporation; Carboxymethyl cellulose (CMC): CMC-NaFH9 (viscosity 1000-2000 mPa) (s, 2% aqueous solution) industrial grade, purchased from Aladdin Reagent (Shanghai) Co., Ltd.; Lithium-ion battery electrolyte: 1 mol / L LiPF6-EC / DMC / EMC (volume ratio 1:1:1), battery grade, purchased from Guangzhou Tinci Advanced Materials Co., Ltd. Lithium cobalt oxide (LiCoO2): cathode material, ≥99.5%, purchased from Hunan Yuneng New Energy Battery Materials Co., Ltd. Conductive carbon black: SuperP, battery grade, purchased from Timcal, Switzerland; Lithium metal sheet: 0.3mm thick, battery grade, purchased from Tianjin Zhongneng Lithium Industry Co., Ltd.; Battery casing (CR2032): Stainless steel, standard snap-on type, purchased from Shenzhen BAK Battery Co., Ltd.

[0037] Example 1

[0038] This embodiment discloses an adhesive for flame-retardant ceramic-coated diaphragms, which is prepared according to the following method: Step 1: Add 0.082 mol of PPO to a three-necked flask containing 150 mL of chlorobenzene, stir and heat to 80 °C to completely dissolve the PPO; then add 8.02 g of NBS (0.045 mol) and 0.216 g of BPO to the three-necked flask, heat to 110 °C, and bromination reaction under nitrogen protection for 6 h to obtain the reaction product; add 300 mL of anhydrous ethanol to the reaction product for precipitation and washing, repeat the precipitation and washing three times, transfer the precipitate to an oven and vacuum dry at 60 °C for 12 h to obtain 17.62 g of brominated polyphenylene ether (0.043 mol). Step 2: Add 17.62g of brominated polyphenylene ether to a three-necked flask containing 200mL of DMF and stir until completely dissolved. Then add 13.87g of P(OEt)3 (0.090mol), heat to 140℃, and carry out a phosphate ester synthesis reaction for 8h under nitrogen protection to obtain the reaction product. Add 400mL of petroleum ether to the reaction product for precipitation and washing. Repeat the precipitation and washing three times. Transfer the precipitate to an oven and vacuum dry at 60℃ for 12h to obtain 18.7g of phosphorylated polyphenylene ether containing phosphate ester groups, which is used as a binder (P-PPO).

[0039] Example 2

[0040] This embodiment discloses an adhesive for flame-retardant ceramic-coated diaphragms, which is prepared according to the following method: Step 1: Add 10g of PPO (0.082mol) to a three-necked flask containing 150mL of chlorobenzene, stir and heat to 80℃ to completely dissolve the PPO; then add 5.84g of NBS (0.0328mol) and 0.127g of BPO to the three-necked flask, heat to 100℃, and bromine reaction under nitrogen protection for 4h to obtain the reaction product; add 300mL of anhydrous ethanol to the reaction product for precipitation and washing, repeat the precipitation and washing three times, transfer the precipitate to an oven and vacuum dry at 60℃ for 12h to obtain 15.49g of brominated polyphenylene ether (0.0308mol). Step 2: Add 15.49 g of brominated polyphenylene ether to a three-necked flask containing 200 mL of DMF and stir until completely dissolved. Then add 7.60 g of P(OEt)3 (0.0493 mol), heat to 130 °C, and carry out a phosphate ester synthesis reaction for 6 h under nitrogen protection to obtain the reaction product. Add 400 mL of petroleum ether to the reaction product for precipitation and washing. Repeat the precipitation and washing three times. Transfer the precipitate to an oven and dry it under vacuum at 60 °C for 12 h to obtain 16.29 g of phosphorylated polyphenylene ether containing phosphate ester groups, which is used as a binder (P-PPO).

[0041] Example 3

[0042] This embodiment discloses an adhesive for flame-retardant ceramic-coated diaphragms, which is prepared according to the following method: Step 1: Add 10g of PPO (0.082mol) to a three-necked flask containing 150mL of chlorobenzene, stir and heat to 80℃ to completely dissolve the PPO; then add 11.67g of NBS (0.0656mol) and 0.39g of BPO to the three-necked flask, heat to 130℃, and bromine under nitrogen protection for 10h to obtain the reaction product; add 300mL of anhydrous ethanol to the reaction product for precipitation and washing, repeat the precipitation and washing three times, transfer the precipitate to an oven and vacuum dry at 60℃ for 12h to obtain 20.85g of brominated polyphenylene ether (0.061mol). Step 2: Add 20.85g of brominated polyphenylene ether to a three-necked flask containing 200mL of DMF and stir until completely dissolved. Then add 28.21g of P(OEt)3 (0.183mol), heat to 160℃, and carry out a phosphate ester synthesis reaction for 12h under nitrogen protection to obtain the reaction product. Add 400mL of petroleum ether to the reaction product for precipitation and washing. Repeat the precipitation and washing three times. Transfer the precipitate to an oven and vacuum dry at 60℃ for 12h to obtain 22.4g of phosphorylated polyphenylene ether containing phosphate ester groups, which is used as a binder (P-PPO).

[0043] Example 4

[0044] This embodiment discloses an adhesive for flame-retardant ceramic-coated diaphragms, which is prepared according to the following method: Step 1 is exactly the same as step 1 in Example 1; Step 2 is exactly the same as step 2 in Example 1; Step 3: Take 18g of phosphorylated polyphenylene ether containing phosphate ester groups and add it to a three-necked flask containing 50mL of concentrated hydrochloric acid solution with a mass fraction of 37%. Stir and heat to 70℃ and hydrolyze for 4h. After the reaction is completed, cool to room temperature and neutralize the reaction solution with 10% sodium hydroxide solution to pH=7. Filter to remove salt precipitate. Add the filtrate dropwise to 200mL of anhydrous ethanol to precipitate. After filtration, wash the precipitate 3 times with distilled water and then transfer it to an oven and vacuum dry at 60℃ for 12h to obtain 17.1g of phosphorylated polyphenylene ether containing phosphate groups, which is used as binder (P-PPO).

[0045] Example 5

[0046] This embodiment discloses an adhesive for flame-retardant ceramic-coated diaphragms, which is prepared according to the following method: Step 1 is exactly the same as step 1 in Example 1; Step 2 is exactly the same as step 2 in Example 1; Step 3: Add 16g of phosphorylated polyphenylene ether containing phosphate ester groups to a three-necked flask containing 40mL of 45% hydrogen bromide solution, stir and heat to 75℃, and hydrolyze for 5h. After the reaction is complete, cool to room temperature, neutralize the reaction solution with 10% sodium bicarbonate solution to pH=7, filter to remove salt precipitate, add the filtrate dropwise to 200mL of anhydrous ethanol to precipitate, filter and wash the precipitate 3 times with distilled water, then transfer to an oven and vacuum dry at 60℃ for 12h to obtain 15.0g of phosphorylated polyphenylene ether containing phosphate groups, which is used as binder (P-PPO).

[0047] Comparative Example 1

[0048] Commercially available polyvinylidene fluoride (PVDF) was used as the binder in this comparative example.

[0049] Comparative Example 2

[0050] Commercially available styrene-butadiene rubber (SBR) was used as the binder in this comparative example.

[0051] Comparative Example 3

[0052] Commercially available carboxymethyl cellulose (CMC) was used as the binder in this comparative example.

[0053] Flame-retardant ceramic-coated membranes were prepared using the binders from Examples 1-5 and Comparative Examples 1-3, respectively. The preparation methods are as follows: Step 1: In a stirred tank, Al2O3 particles, binder and polyethylene glycol (dispersant) are dispersed in a solvent (a mixture of water and anhydrous ethanol in a volume ratio of 5:1). The mass ratio of Al2O3 particles, P-PPO, polyethylene glycol and solvent is 100:51:150. After stirring evenly, the mixture is transferred to a ball mill and milled for 4 hours using zirconia balls as the grinding medium (ball-to-material ratio of 5:1) to obtain a uniform ceramic slurry with a solid content of 40%. Step 2: Use a doctor blade coating method to evenly coat the ceramic slurry on both sides of a PE base film with a thickness of 12 μm. Adjust the doctor blade gap to 30 μm and the coating speed to 2 m / min to ensure uniform coating thickness. Step 3: Place the PE base film in an oven and dry it at 60℃ for 30 minutes, then raise the temperature to 100℃ and dry it for 60 minutes to remove the solvent; after cooling to room temperature, a double-sided ceramic coated diaphragm is obtained, with a coating thickness of 2.5μm on one side and a total thickness of about 17μm and a porosity of 38%.

[0054] The flame retardant properties, adhesive strength, thermal shrinkage rate, and rupture temperature of the obtained PE base film coated with flame-retardant ceramic diaphragm on both sides were tested. The test methods were as follows: Flame retardancy test: Refer to UL94 vertical bond strength direct combustion test standard (GB / T2408-2021); take 5 samples each in the longitudinal and transverse directions of the diaphragm, with a size of 127mm×12.7mm (thickness is the actual total coating thickness), with no burrs on the edges and no coating peeling; equilibrate for 24h in an environment of 23℃±2℃ and relative humidity of 50%±5%; use a vertical combustion tester, suspend the sample vertically with a clamp (clamping the upper end 10mm), and the lower end of the sample is 300mm away from the degreased cotton; the tip of the flame contacts the lower end of the sample 10mm away, ignite for 10s and then remove it, and record the first flaming combustion time (t1); immediately after the first combustion is extinguished, ignite again for 10s, and record the second flaming combustion time (t2) and the flameless combustion time (t3); observe whether there are burning drips and whether the degreased cotton is ignited; V-0 grade must meet the following: t1 and t2 are both ≤10s, t3≤30s, no ignitable drips, and char length ≤50mm.

[0055] Adhesion strength test: Refer to "Test method for 180° peel strength of adhesives" (GB / T2792-2014); take 5 samples, size 150mm×25mm (total thickness about 17μm); bond the back of the PE base film to the stainless steel substrate with epoxy adhesive and cure at 60℃ for 2h; pre-peel 10mm from one end of the sample to form the starting end, and equilibrate for 24h in an environment of 23℃±2℃ and relative humidity of 50%±5%; set the universal tensile testing machine to test temperature 23℃±2℃, peel speed 300mm / min, and sensor range 0-50N; the upper clamp of the tensile testing machine holds the starting end of the coating, and the lower clamp holds the stainless steel substrate, maintaining a 180° peel angle; start the equipment, peel to a length of 100mm, and record the average force value (F_avg) within the middle 80mm range; peel strength (N / cm) = average force value (F_avg) ÷ actual width of sample (cm) (width is the average value of the measurements at the front, middle, and back points), and the final result is the average value of the 5 samples.

[0056] Heat shrinkage rate: Refer to the "Test method for dimensional change rate of plastic films and sheets under heating" (GB / T 12027-2004), take a 100mm×100mm ceramic-coated diaphragm sample, let it stand in a constant temperature oven at 200℃ for 1h, and after cooling to room temperature, measure the change in length / width of the sample and calculate the heat shrinkage rate (take the average value of longitudinal and transverse). Rupture temperature: A thermomechanical analyzer (TMA, model TA Q400) was used to heat the membrane from room temperature to 300°C at a rate of 5°C / min, and the temperature at which the membrane ruptured due to thermal runaway was recorded (i.e., rupture temperature).

[0057] The test results are listed in Table 1, as follows: Table 1

[0058] Analysis of the data in Table 1 shows that the flame retardant performance of Examples 1-5 all meets the UL94V-0 flame retardant standard, while Comparative Examples 1-3 only meet the UL94V-1 flame retardant standard. This indicates that compared with PVDF, SBR, and CMC binders in the prior art, the P-PPO binder of the present invention has stronger flame retardant performance. This may be because the phosphorus-containing functional groups in the P-PPO binder decompose to generate non-volatile phosphoric acid during combustion, which promotes the carbonization of Al2O3 particles and polymer surfaces, forming a dense heat-insulating carbon layer, blocking the transfer of oxygen and heat, and achieving a self-extinguishing effect.

[0059] The peel strength of Examples 1-5 was 1.48 N / cm or higher, which was significantly higher than that of Comparative Examples 1-3. Among them, the peel strength of Examples 4-5 was significantly higher than that of Examples 1-3, and all were much higher than that of Comparative Examples 1-3. This may be because the phosphate groups / phosphate ester groups in P-PPO form strong hydrogen bonds and coordination bonds with the hydroxyl groups on the surface of Al2O3 particles, achieving chemical anchoring; and the phosphate groups have more hydroxyl groups and stronger interaction with the hydroxyl groups, thus resulting in higher bonding strength.

[0060] The membranes of Examples 1-5 exhibited thermal shrinkage rates between 1.1% and 1.6% under 200℃×1h conditions, which are significantly lower than 2% and substantially better than those of Comparative Examples 1-3. This may be because the glass transition temperature of the main skeleton (PPO) of phosphorylated polyphenylene ether (P-PPO) is approximately 210℃, which allows it to maintain rigidity even at 200℃, thus preventing the base film from shrinking. The chemical anchoring effect formed by the phosphorus-containing functional groups and ceramic particles (Al2O3) ensures a tight bond between the coating and the base film, inhibiting the free shrinkage of the base film at high temperatures. Simultaneously, the dense carbon layer formed by the decomposition of phosphorus-containing functional groups at high temperatures further supports the membrane structure and reduces thermal deformation.

[0061] The membrane breaking temperatures of Examples 1-5 were all between 225℃ and 250℃, while the membrane breaking temperature of the comparative example was only 165℃-180℃, which could not withstand the risk of high temperature. The examples were significantly better than the comparative example. This may be because the high molecular weight characteristics of P-PPO ensure the entanglement strength between molecular chains, making them less prone to breakage at high temperatures. The moderate degree of modification balances the grafting density of phosphorus-containing functional groups with the integrity of the main skeleton, preserving the heat resistance of PPO while enhancing structural stability through the functional group effect. Moreover, the strong adhesion between the ceramic coating and the base film prevents the base film from breaking due to heat exposure caused by coating peeling at high temperatures.

[0062] Lithium batteries were prepared using PE base films with flame-retardant ceramic-coated separators on both sides, as shown in Examples 1-5 and Comparative Examples 1-3. The preparation methods are as follows: Step 1: Prepare raw materials according to the mass ratio of LiCoO2:conductive carbon black:PVDF = 8:1:1, add NMP solvent, and stir to form a uniform positive electrode slurry; coat the slurry onto an aluminum foil current collector, pre-dry at 60℃ for 30 min, vacuum dry at 120℃ for 12 h, roll press and cut into positive electrode sheets with a diameter of 14 mm and a compaction density of 3.6 g / cm³. 3 Thus, a positive electrode sheet is obtained; Step 2: Use a 16mm diameter lithium metal sheet as the negative electrode. Step 3: In an argon glove box (water and oxygen content ≤1ppm), assemble the CR2032 button battery case, positive electrode, PE base film (18mm in diameter) coated with flame-retardant ceramic coating on both sides, electrolyte (50μL added to each battery), lithium metal sheet, gasket, spring sheet, and battery cover in sequence, press and seal to obtain a button lithium-ion battery.

[0063] The obtained lithium battery was subjected to electrochemical performance testing. The testing method was as follows: Initial charge and discharge performance: Using a battery testing system (model CT2001A, Wuhan Landian Electronics Co., Ltd.), constant current charge and discharge were performed at a rate of 0.2C (1C=140mA / g) at 25℃. The charging cutoff voltage was 4.3V and the discharging cutoff voltage was 3.0V. The initial charge capacity and initial discharge capacity were recorded. Rate performance: At 25℃, the battery was activated by charging and discharging twice at a rate of 0.2C. Then, constant current discharge was performed at rates of 0.2C, 0.5C, 1C, 2C, and 5C (after each discharge, the battery was charged to 4.3V at a rate of 0.2C). The discharge capacity at each rate was recorded, and the retention rate of the discharge capacity at different rates relative to the discharge capacity at the 0.2C rate was calculated. Cyclic performance: Under 25℃ conditions, constant current charge-discharge cycle test was performed at 1C rate (charging cut-off voltage 4.3V, discharging cut-off voltage 3.0V). The discharge capacity after 500 cycles was recorded, and the capacity retention rate was calculated (discharge capacity after 500 cycles ÷ initial discharge capacity × 100%).

[0064] The test results are listed in Table 2, as follows: Table 2

[0065] Analysis of the data in Table 2 shows that, compared with Comparative Examples 1-3, the initial discharge capacity of Examples 1-5 is significantly higher, all above 140 mAh / g. This may be because the phosphate / phosphate ester groups in the P-PPO binder are strongly polar groups, which significantly improve the wettability of the ceramic coating to the electrolyte, shorten the wetting time, and make the lithium ion transport channel smoother, thus resulting in a higher initial discharge capacity. In contrast, PVDF has weak polarity, and the electrolyte wetting is insufficient, resulting in a lower capacity.

[0066] Compared to Comparative Examples 1-3, Examples 1-5 showed significantly higher 5C / 0.2C capacity retention rates, all above 75%. This may be because, during high-rate discharge, the lithium-ion transport rate is required to be high, and the high electrolyte affinity and good pore structure of the P-PPO coating ensure rapid lithium-ion migration.

[0067] Compared to Comparative Examples 1-3, Examples 1-5 showed significantly higher capacity retention after 500 cycles, all exceeding 84%. This may be because, on the one hand, the strong adhesion of the P-PPO binder prevented the ceramic coating from peeling off during cycling, ensuring the stability of the membrane structure; on the other hand, the high glass transition temperature of the PPO main skeleton enabled the membrane to maintain dimensional stability under the mild temperature rise environment of cyclic charging and discharging, reducing the increase in lithium-ion transport resistance, thus resulting in excellent cycling performance.

[0068] The foregoing has described several embodiments of the present invention in detail, but these descriptions are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. An adhesive for flame-retardant ceramic-coated diaphragms, characterized in that, The active ingredient of the binder is phosphorylated polyphenylene ether, which is a functional polymer obtained by introducing phosphorus-containing functional groups into the main chain and / or side chain of polyphenylene ether.

2. The adhesive for flame-retardant ceramic-coated diaphragms according to claim 1, characterized in that, The phosphorus-containing functional group is at least one of a phosphate group, a phosphate ester group, or a phosphate group.

3. A preparation method for preparing the adhesive for flame-retardant ceramic-coated diaphragms as described in any one of claims 1-2, characterized in that, Includes the following steps: Step 1: Dissolve poly(2,6-dimethyl-1,4-phenyl ether) in a high-boiling-point solvent, add N-bromosuccinimide and an initiator, and carry out a side-chain bromination reaction at 90-130℃ to obtain the reaction product; add alcohol to the reaction product for precipitation washing and drying to obtain brominated polyphenyl ether; Step 2: Dissolve the brominated polyphenylene ether in an aprotic solvent, add triethyl phosphite, wherein the amount of triethyl phosphite added is 1.2-3.0 times the molar amount of the brominated polyphenylene ether; carry out the phosphate ester synthesis reaction at 120-160℃ to obtain the reaction product; add a non-solvent to the reaction product for precipitation washing and drying to obtain phosphorylated polyphenylene ether containing phosphate ester groups.

4. The preparation method according to claim 3, characterized in that, Also includes: Step 3: Add the phosphorylated polyphenylene ether containing phosphate ester groups to concentrated hydrochloric acid or hydrogen bromide solution and heat to hydrolyze. Neutralize the hydrolysate with alkaline solution to pH=6-7, filter, wash and dry to obtain phosphorylated polyphenylene ether containing phosphate groups.

5. The preparation method according to claim 3, characterized in that, In step 1, the high-boiling-point solvent is chlorobenzene.

6. The preparation method according to claim 3, characterized in that, In step 1, the molar ratio of poly(2,6-dimethyl-1,4-phenyl ether) to N-bromosuccinimide is 1:(0.3-0.8).

7. The preparation method according to claim 6, characterized in that, In step 1, the initiator is benzoyl peroxide, and the amount of benzoyl peroxide added is 0.5-2 wt% of the sum of the mass of poly(2,6-dimethyl-1,4-phenyl ether) and N-bromosuccinimide.

8. The preparation method according to claim 3, characterized in that, In step 2, the aprotic solvent is at least one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide.

9. The preparation method according to claim 4, characterized in that, In step 3, if a concentrated hydrochloric acid solution is used, the mass fraction of hydrochloric acid in the concentrated hydrochloric acid solution is 36-38%; if a hydrogen bromide solution is used, the mass fraction of hydrogen bromide in the hydrogen bromide solution is 40-48%.

10. The preparation method according to claim 3, characterized in that, In step 1, the bromination reaction takes 2-10 hours; in step 2, the phosphate ester synthesis reaction takes 4-12 hours.

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