A surface-modified diaphragm and its preparation method

Abstract

This application discloses a method for preparing a surface-modified separator in the field of lithium-ion battery technology, including the following steps: S1, surface modification of nano-Al2O3: nano-Al2O3 is made into a suspension, a silane coupling agent is dissolved in ethanol and added dropwise to the suspension at a certain rate, and the reaction is carried out in an inert gas environment. After the reaction is completed, the Al2O3 precipitate is washed and dried to obtain pre-modified nano-Al2O3; the pre-modified nano-Al2O3 is added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid, and after the reaction is completed, the precipitate is washed and dried to obtain modified nano-Al2O3 with free radical functional groups; S2, substrate pre-irradiation; S3, separator surface grafting treatment; S4, ceramic particle coating: the modified nano-Al2O3 is dissolved and a binder is added to obtain a ceramic particle slurry, and the ceramic particle slurry is coated on the grafted modified separator to obtain the surface-modified separator. This application improves the hydrophilicity and wettability of the separator substrate, and significantly improves the rate and cycle performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a surface-modified separator and its preparation method. Background Technology

[0002] The separator is one of the key components of a lithium-ion battery. During battery use, the separator maintains the relative positions of the cells, preventing direct contact and short circuits between the positive and negative electrodes, and providing pathways for the smooth migration of lithium ions during charging and discharging. The chemical stability, thermal stability, mechanical strength, and porosity of the lithium-ion battery separator have a significant impact on the performance, safety, and lifespan of the lithium-ion battery.

[0003] Radiation grafting of separators is a method for preparing battery separators using radiation grafting technology. It involves generating active sites in polymer separator materials through high-energy radiation and grafting functional monomers onto these sites, thereby endowing the separator with new chemical and physical properties. Radiation grafting can significantly improve the hydrophilicity and wettability of the separator, facilitating ion transport, enhancing the electrochemical performance of lithium-ion batteries, increasing the separator's durability under different environments, improving the compatibility of the separator with other components such as electrode materials, and optimizing the overall battery performance. However, most existing grafting modification processes involve direct grafting onto the separator surface or the surface of inorganic ceramic materials without any surface treatment, resulting in incomplete grafting reactions of functional monomers. The pre-radiation treatment method used in this application not only makes the connection structure formed by the trapped groups and the grafted groups on the surface of the inorganic ceramic particles more stable, but the provided trapped particles and unreacted trapped groups also further enhance the hydrophilicity and wettability of the separator substrate. Summary of the Invention

[0004] The present invention aims to provide a surface-modified diaphragm and its preparation method, which not only makes the connection structure formed by the trapped groups and the grafted groups on the surface of inorganic ceramic particles more stable, but also further improves the hydrophilicity and wettability of the diaphragm substrate by providing the trapped particles and the unreacted trapped groups.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a surface-modified diaphragm includes the following steps:

[0007] S1. Surface modification of nano-Al2O3: Nano-Al2O3 is made into a suspension, and a silane coupling agent is dissolved in ethanol and added dropwise to the suspension at a certain rate. The reaction is carried out in an inert gas environment. After the reaction is completed, the Al2O3 precipitate is washed and dried to obtain preliminarily modified nano-Al2O3. The preliminarily modified nano-Al2O3 is added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid. After the reaction is completed, the precipitate is washed and dried to obtain modified nano-Al2O3 with free radical functional groups.

[0008] S2. Substrate pre-irradiation: The radiation bag is filled with inert gas, the diaphragm is sealed in the radiation bag, and the sealed bag is placed in the radiation field and then removed.

[0009] S3. Grafting treatment on the surface of the diaphragm: The irradiated diaphragm is added to an organic solvent, a solvent, concentrated sulfuric acid and a reaction inhibitor, and an inert gas is introduced at room temperature. Then the reaction is carried out under water bath heating conditions. After the reaction is completed, the diaphragm is washed and dried to obtain the grafted modified diaphragm.

[0010] S4. Coating of ceramic particles: Dissolve the modified nano-Al2O3 and add a binder to obtain a ceramic particle slurry. Coat the ceramic particle slurry onto the grafted modified diaphragm to obtain a surface-modified diaphragm.

[0011] Working principle and beneficial effects of the present invention:

[0012] In this application, after treatment with a coupling agent, the inorganic ceramic particles in S1 have a large number of surface-active functional groups on their surface, which is beneficial for their combination with the pre-radiation treated substrate. The free radical groups are oxidizing groups, which is beneficial for improving the hydrophilicity of nano-Al2O3. In S2, the pre-radiation substrate promotes the coating and hydrophilicity of the ceramic membrane. In S3, irradiation of the PE membrane generates alkyl free radicals, allyl free radicals and polyolefin free radicals. After adding grafted monomers to methanol, the free radicals generated under the action of a catalyst react with the radiation-generated free radicals to form new products. The new products refer to products such as water and graft copolymers formed by the combination of the two groups. The branched structure formed by the chemical reaction allows the free radical monomer molecules of the irradiated PE membrane to combine with the main chain. Compared with the original membrane, the grafted membrane is more conducive to surface coating and has better adhesion.

[0013] The pre-radiation treatment method for the separator used in this application not only makes the connection structure formed by the trapped groups and the grafted groups on the surface of the inorganic ceramic particles more stable, but also provides trapped particles and unreacted trapped groups to further improve the hydrophilicity and wettability of the separator substrate, significantly improving the rate and cycle performance of the battery.

[0014] In an optimized manner, S1 dries the nano-Al2O3, adds ethanol, and ultrasonically disperses it into a nano-Al2O3 suspension. The suspension is then heated to 40–70°C and connected to a reflux condenser.

[0015] Optimally, the silane coupling agent is KH570. The silane coupling agent is added dropwise to the nano-Al2O3 suspension at a rate of 2-3 ml / min, and the reaction is carried out in an inert gas environment for 12-24 h. After the reaction is completed, the Al2O3 precipitate is washed 3-5 times with anhydrous ethanol and dried to obtain the preliminarily modified nano-Al2O3.

[0016] In an optimized manner, S1 is added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, and the reaction is carried out at 60-80℃ for 12-24 hours. After the reaction is completed, the Al2O3 precipitate is washed 3-5 times with anhydrous ethanol and dried to obtain modified nano-Al2O3 with free radical functional groups.

[0017] Ideally, the S2 radiation uses Co60–γ rays, with a radiation dose of 50–150 kGy, a radiation time of 4–12 h, a radiation electron beam of 0.5–2 MeV, a radiation electron current of 0.5–5 mA, an inert gas of nitrogen or argon, and a diaphragm made of PE or PP material with a thickness of 6–15 μm.

[0018] Optimally, the organic solvent is oleic acid, acrylic acid, or hydroxymethylacrylic acid, the solvent is deionized water or methanol, and the reaction inhibitor is one or more of copper sulfate, ferrous ammonium sulfate, or metal salts.

[0019] Ideally, S3 is introduced with an inert gas at room temperature for 20–30 min, followed by reaction under water bath heating for 4–6 h. After the reaction is complete, the membrane is washed 3–5 times with a mixture of deionized water and ethanol, and then dried for 8–10 h to obtain the grafted modified membrane.

[0020] In an optimized manner, S3 is added to deionized water to dissolve the modified nano-Al2O3, lithium polyacrylate binder is added, and ultrasonic dispersion is performed to obtain a slurry of modified nano-Al2O3 ceramic particles.

[0021] Optimally, S4 uses a scraper to coat one side of the grafted modified diaphragm with a slurry of modified nano-Al2O3 ceramic particles, and after drying, coats the other side of the grafted modified diaphragm in the same manner. Attached Figure Description

[0022] Figure 1 This is a graph showing the rate performance of the diaphragm.

[0023] Figure 2 This is a graph showing the cyclic performance. Detailed Implementation

[0024] The following detailed description illustrates the specific implementation method:

[0025] Example 1 (Pre-irradiated membrane substrate + nano-Al2O3):

[0026] Substrate pre-irradiation: The irradiation used in this study is Co60-γ rays, with a radiation dose of 50-150 kGy, an irradiation time of 4-12 h, an electron beam of 0.5-2 MeV, an electron current of 0.5-5 mA, an inert gas of nitrogen or argon, and a diaphragm of PE or PP material with a thickness of 6-15 μm.

[0027] Before starting the equipment, soak the cut diaphragm in acetone for 12 hours, then soak it in deionized water for 12 hours. Finally, wash it with deionized water, dry it, and put it into a radiation bag. Fill the bag with inert gas and seal it in a radiation polyethylene bag. Then place the sealed bag in the radiation field and irradiate for 4-12 hours. After that, take it out and store it in a freeze dryer.

[0028] Coating of ceramic particles: 13.50g of nano Al2O3 was added to 300ml of deionized water and stirred for 12h. After ultrasonic dispersion for 1h, 1.5g of lithium polyacrylate binder was added and stirred for 4h. After ultrasonic dispersion for 30min, Al2O3 ceramic particle slurry was obtained. The slurry was coated on one side of the membrane using a scraper. The prepared membrane was dried in a vacuum oven at 70℃ for 8h. Then the other side was coated in the same way to obtain the membrane of Example 1.

[0029] Example 2 (Modified nano-Al2O3 coating + membrane pre-irradiation):

[0030] Substrate pre-irradiation: The irradiation used in this study is Co60-γ rays, with a radiation dose of 50-150 kGy, an irradiation time of 4-12 h, an electron beam of 0.5-2 MeV, an electron current of 0.5-5 mA, an inert gas of nitrogen or argon, and a diaphragm of PE or PP material with a thickness of 6-15 μm.

[0031] Before starting the equipment, soak the cut diaphragm in acetone for 12 hours, then soak it in deionized water for 12 hours. Finally, wash it with deionized water, dry it, and put it into a radiation bag. Fill the bag with inert gas and seal it in a radiation polyethylene bag. Then place the sealed bag in the radiation field and irradiate for 4-12 hours. After that, take it out and store it in a freeze dryer.

[0032] Surface modification of nano-Al2O3: 100g of nano-Al2O3 was dried at 100℃ for 12h, then placed in a flask, 350ml of ethanol was added, and the mixture was ultrasonically dispersed for 30min to form a nano-Al2O3 suspension. The suspension was then heated to 40-70℃ and connected to a reflux condenser. 1.14g of silane coupling agent KH570 was dissolved in 50ml of ethanol and added dropwise to the nano-Al2O3 suspension at a rate of 2ml / min. The reaction was carried out under an inert gas environment for 12-24h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain preliminarily modified nano-Al2O3.

[0033] The preliminarily modified nano-Al2O3 was placed in a flask and 200 ml of a mixed solvent of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 was added. The mixture was reacted at 60-80℃ for 12-24 h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain modified nano-Al2O3 with free radical functional groups.

[0034] Coating of ceramic particles: 13.50g of modified nano Al2O3 was added to 300ml of deionized water, stirred for 12h, ultrasonically dispersed for 1h, 1.5g of lithium polyacrylate binder was added, stirred for 4h, and ultrasonically dispersed for 30min to obtain modified nano Al2O3 ceramic particle slurry.

[0035] Coating of ceramic particles: 13.50g of modified nano-Al2O3 was added to 300ml of deionized water and stirred for 12h. After ultrasonic dispersion for 1h, 1.5g of lithium polyacrylate binder was added and stirred for 4h. After ultrasonic dispersion for 30min, modified nano-Al2O3 ceramic particle slurry was obtained. The slurry was coated on one side of the diaphragm using a scraper. The prepared diaphragm was dried in a vacuum oven at 70℃ for 8h. Then the other side was coated in the same way to obtain the diaphragm of Example 2.

[0036] Example 3 (Technical solution of this application: modified nano-Al2O3 coating + membrane pre-radiation + membrane surface grafting treatment):

[0037] Substrate pre-irradiation: The irradiation used in this study is Co60-γ rays, with a radiation dose of 50-150 kGy, an irradiation time of 4-12 h, an electron beam of 0.5-2 MeV, an electron current of 0.5-5 mA, an inert gas of nitrogen or argon, and a diaphragm of PE or PP material with a thickness of 6-15 μm.

[0038] Before starting the equipment, soak the cut diaphragm in acetone for 12 hours, then soak it in deionized water for 12 hours. Finally, wash it with deionized water, dry it, and put it into a radiation bag. Fill the bag with inert gas and seal it in a radiation polyethylene bag. Then place the sealed bag in the radiation field and irradiate for 4-12 hours. After that, take it out and store it in a freeze dryer.

[0039] 10.0 g of irradiated PE membrane was added to a mixed solvent of 250 ml methanol, 250 ml 0.8 mol / L concentrated sulfuric acid, 150 ml oleic acid, and 10 ml 0.0004 mol / L copper sulfate. An inert gas was introduced at room temperature for 20-30 min, followed by reaction in a water bath for 4-6 h. After the reaction was complete, the membrane was washed 3-5 times with a mixed solvent of deionized water and ethanol, and then dried at 60 °C for 8-10 h to obtain the grafted modified membrane.

[0040] Surface modification of nano-Al2O3: 100g of nano-Al2O3 was dried at 100℃ for 12h, then placed in a flask, 350ml of ethanol was added, and the mixture was ultrasonically dispersed for 30min to form a nano-Al2O3 suspension. The suspension was then heated to 40-70℃ and connected to a reflux condenser. 1.14g of silane coupling agent KH570 was dissolved in 50ml of ethanol and added dropwise to the nano-Al2O3 suspension at a rate of 2ml / min. The reaction was carried out under an inert gas environment for 12-24h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain preliminarily modified nano-Al2O3.

[0041] The preliminarily modified nano-Al2O3 was placed in a flask and 200 ml of a mixed solvent of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 was added. The mixture was reacted at 60-80℃ for 12-24 h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain modified nano-Al2O3 with free radical functional groups.

[0042] Coating of ceramic particles: 13.50g of modified nano-Al2O3 was added to 300ml of deionized water, stirred for 12h, ultrasonically dispersed for 1h, 1.5g of lithium polyacrylate binder was added, stirred for 4h, and ultrasonically dispersed for 30min to obtain a slurry of modified nano-Al2O3 ceramic particles; the slurry was coated on one side of the diaphragm using a scraper, and the prepared diaphragm was dried in a vacuum oven at 70℃ for 8h. Then the other side was coated in the same way to obtain the diaphragm of Example 3.

[0043] Example 4 (Nano Al2O3 + membrane pre-irradiation + membrane surface grafting treatment):

[0044] Substrate pre-irradiation: The irradiation used in this study is Co60-γ rays, with a radiation dose of 50-150 kGy, an irradiation time of 4-12 h, an electron beam of 0.5-2 MeV, an electron current of 0.5-5 mA, an inert gas of nitrogen or argon, and a diaphragm of PE or PP material with a thickness of 6-15 μm.

[0045] Before starting the equipment, soak the cut diaphragm in acetone for 12 hours, then soak it in deionized water for 12 hours. Finally, wash it with deionized water, dry it, and put it into a radiation bag. Fill the bag with inert gas and seal it in a radiation polyethylene bag. Then place the sealed bag in the radiation field and irradiate for 4-12 hours. After that, take it out and store it in a freeze dryer.

[0046] 10.0 g of irradiated PE membrane was added to a mixed solvent of 250 ml methanol, 250 ml 0.8 mol / L concentrated sulfuric acid, 150 ml oleic acid, and 10 ml 0.0004 mol / L copper sulfate. An inert gas was introduced at room temperature for 20-30 min, followed by reaction in a water bath for 4-6 h. After the reaction was complete, the membrane was washed 3-5 times with a mixed solvent of deionized water and ethanol, and then dried at 60 °C for 8-10 h to obtain the grafted modified membrane.

[0047] Coating of ceramic particles: 13.50g of nano Al2O3 was added to 300ml of deionized water and stirred for 12h. After ultrasonic dispersion for 1h, 1.5g of lithium polyacrylate binder was added and stirred for 4h. After ultrasonic dispersion for 30min, Al2O3 ceramic particle slurry was obtained. The slurry was coated on one side of the membrane using a scraper. The prepared membrane was dried in a vacuum oven at 70℃ for 8h. Then the other side was coated in the same way to obtain the membrane of Example 4.

[0048] Example 5 (Modified nano-Al2O3 coating + membrane):

[0049] Surface modification of nano-Al2O3: 100g of nano-Al2O3 was dried at 100℃ for 12h, then placed in a flask, 350ml of ethanol was added, and the mixture was ultrasonically dispersed for 30min to form a nano-Al2O3 suspension. The suspension was then heated to 40-70℃ and connected to a reflux condenser. 1.14g of silane coupling agent KH570 was dissolved in 50ml of ethanol and added dropwise to the nano-Al2O3 suspension at a rate of 2ml / min. The reaction was carried out under an inert gas environment for 12-24h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain preliminarily modified nano-Al2O3.

[0050] The preliminarily modified nano-Al2O3 was placed in a flask and 200 ml of a mixed solvent of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1 was added. The mixture was reacted at 60-80℃ for 12-24 h. After the reaction was completed, the Al2O3 precipitate was washed 3-5 times with anhydrous ethanol and dried at 60℃ to obtain modified nano-Al2O3 with free radical functional groups.

[0051] Coating of ceramic particles: 13.50g of modified nano-Al2O3 was added to 300ml of deionized water, stirred for 12h, ultrasonically dispersed for 1h, 1.5g of lithium polyacrylate binder was added, stirred for 4h, and ultrasonically dispersed for 30min to obtain a slurry of modified nano-Al2O3 ceramic particles; the slurry was coated on one side of the untreated diaphragm using a scraper, and the prepared diaphragm was dried in a vacuum oven at 70℃ for 8h. Then the other side was coated in the same way to obtain the diaphragm of Example 5.

[0052] The diaphragms prepared in Examples 1 to 5 were subjected to rate performance and cycle tests, such as... Figure 1 and Figure 2 As shown, from Figure 1 and Figure 2 As can be seen, the surface-modified ceramic separator for lithium-ion batteries prepared by pre-radiation grafting in Example 3 outperforms the separators of Examples 1, 2, 4, and 5 in terms of rate performance and cycle life. That is, this application further improves the hydrophilicity and wettability of the separator substrate, significantly improving the rate and cycle performance of the battery.

Claims

1. A method for preparing a surface-modified diaphragm, characterized in that, Includes the following steps, S1. Surface modification of nano-Al2O3: Nano-Al2O3 is made into a suspension, and a silane coupling agent is dissolved in ethanol and added dropwise to the suspension at a certain rate. The reaction is carried out in an inert gas environment. After the reaction is completed, the Al2O3 precipitate is washed and dried to obtain preliminarily modified nano-Al2O3. The preliminarily modified nano-Al2O3 is added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid. After the reaction is completed, the precipitate is washed and dried to obtain modified nano-Al2O3 with free radical functional groups. S2. Substrate pre-irradiation: The radiation bag is filled with inert gas, the diaphragm is sealed in the radiation bag, and the sealed bag is placed in the radiation field and then removed. S3. Grafting treatment of the diaphragm surface: The irradiated diaphragm is added to an organic solvent, a solvent, concentrated sulfuric acid and a reaction inhibitor, and an inert gas is introduced at room temperature. Then, the reaction is carried out under water bath heating conditions. After the reaction is completed, the diaphragm is washed and dried to obtain a grafted modified diaphragm. The organic solvent is oleic acid, acrylic acid or hydroxymethylacrylic acid, the solvent is methanol, and the reaction inhibitor is one or more of copper sulfate, ferrous ammonium sulfate or metal salt. S4. Coating of ceramic particles: Dissolve the modified nano-Al2O3 and add a binder to obtain a ceramic particle slurry. Coat the ceramic particle slurry onto the grafted modified diaphragm to obtain a surface-modified diaphragm.

2. The method for preparing the surface-modified diaphragm according to claim 1, characterized in that, S1. Surface modification of nano-Al2O3: After drying nano-Al2O3, add ethanol and ultrasonically disperse it into a nano-Al2O3 suspension. Heat the suspension to 40-70°C and connect it to a reflux condenser.

3. The method for preparing the surface-modified diaphragm according to claim 2, characterized in that, The silane coupling agent is KH570. The silane coupling agent is added dropwise to the nano-Al2O3 suspension at a rate of 2-3 ml / min. The reaction is carried out in an inert gas environment for 12-24 h. After the reaction is completed, the Al2O3 precipitate is washed 3-5 times with anhydrous ethanol and dried to obtain the preliminarily modified nano-Al2O3.

4. The method for preparing the surface-modified diaphragm according to claim 3, characterized in that, S1. Surface modification of nano-Al2O3: Add a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, and react at 60-80℃ for 12-24h. After the reaction is completed, wash the Al2O3 precipitate with anhydrous ethanol 3-5 times and dry it to obtain modified nano-Al2O3 with free radical functional groups.

5. The method for preparing the surface-modified diaphragm according to claim 4, characterized in that, S2. Substrate pre-irradiation: The irradiation uses Co60 to gamma rays, with a radiation dose of 50 to 150 kGy, an irradiation time of 4 to 12 hours, an electron beam of 0.5 to 2 MeV, an electron current of 0.5 to 5 mA, an inert gas of nitrogen or argon, and a diaphragm of PE or PP material with a thickness of 6 to 15 μm.

6. The method for preparing the surface-modified diaphragm according to claim 5, characterized in that, S3. Grafting treatment of the membrane surface: Inert gas is introduced at room temperature for 20-30 minutes, followed by reaction under water bath heating for 4-6 hours. After the reaction is completed, the membrane is washed 3-5 times with a mixture of deionized water and ethanol, and then dried for 8-10 hours to obtain the grafted modified membrane.

7. The method for preparing the surface-modified diaphragm according to claim 6, characterized in that, S4. Coating of ceramic particles: Add deionized water to dissolve modified nano-Al2O3, add lithium polyacrylate binder, and ultrasonically disperse to obtain modified nano-Al2O3 ceramic particle slurry.

8. The method for preparing the surface-modified diaphragm according to claim 7, characterized in that, S4. Coating of ceramic particles: Use a scraper to coat one side of the grafted modified diaphragm with the modified nano-Al2O3 ceramic particle slurry, and after drying, coat the other side of the grafted modified diaphragm in the same way.

9. The surface-modified diaphragm prepared by the method according to any one of claims 1 to 8.

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