Three-layer composite diaphragm and preparation method thereof

Abstract

The application relates to the technical field of batteries, and discloses a three-layer composite diaphragm and a preparation method thereof. The three-layer composite diaphragm comprises three layers which are sequentially compounded from inside to outside, namely a polyimide base layer, a thermal response layer and an ion sieving functional layer. The thermal response layer of the application takes nano silicon dioxide as a rigid skeleton, and a temperature-sensitive polymer poly (N-isopropyl acrylamide) is grafted on the surface to form a core-shell structure. The porosity is high at low temperature, and the ion conductivity is high. With the increase of temperature, PNIPAM shrinks due to dehydration, the pores are quickly closed, ion transmission is blocked to prevent thermal runaway. In addition, the polyimide base layer provides excellent mechanical tensile strength, the ion sieving layer inhibits polysulfide shuttling and adsorbs HF in the electrolyte, and the three layers jointly act to prolong the service life of the battery and improve the safety.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a three-layer composite diaphragm and a preparation method thereof. BACKGROUND

[0002] The battery diaphragm is a key component in lithium ion batteries, which mainly functions to physically separate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to pass freely to complete the charging and discharging cycle. The functional characteristics of the battery diaphragm directly affect the battery energy density, cycle life and safety, for example, ceramic coating can enhance the anti- dendrite puncture ability. With the development of solid-state batteries, new diaphragms tend to be ultra-thin, such as less than 5 μm, and integrate electrolyte functions. Intelligent diaphragms can also monitor real-time changes in battery internal pressure or temperature, providing protection for the safe operation of high-energy-density batteries.

[0003] The current common diaphragm mainly uses PE and PP as the main body, which has a low thermal deformation temperature. When the temperature is too high, the diaphragm will shrink severely, which can easily cause the positive and negative electrodes of the battery to come into contact and short circuit, and then cause the battery to lose control. Therefore, how to avoid the occurrence of thermal runaway has become the focus of current lithium ion battery research. Patent CN119786879A discloses a lithium ion battery diaphragm modified by high-temperature fluorine-containing liquid crystal polymer and polyvinylidene fluoride and its preparation method and application. The ordered arrangement of the molecular chain of the liquid crystal polymer makes the modified diaphragm have higher mechanical strength and toughness, and can withstand greater stress during the charging and discharging process of the battery. The presence of fluorine groups improves the heat resistance of the material, while maintaining appropriate porosity to ensure smooth conduction of lithium ions, thereby ensuring the safety and life of the battery. Although the diaphragm prepared by this method has high heat resistance, it still cannot avoid the problem of diaphragm shrinkage and deformation at high temperatures leading to battery short circuit and loss of control. SUMMARY

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the present application aims to provide a three-layer composite diaphragm and a preparation method thereof. The prepared diaphragm can dynamically respond to temperature changes and prevent battery loss of control at high temperatures.

[0005] The technical solution adopted by the present application to solve its technical problems is:

[0006] A three-layer composite diaphragm, comprising three layers composed of a polyimide base layer, a thermal response layer and an ion sieving functional layer, from inside to outside.

[0007] The polyimide base layer is composed of polyimide; the thermal response layer is obtained by polymerization of N-isopropyl acrylamide; and the ion sieving layer is composed of zinc nitrate hexahydrate and 2-methylimidazole.

[0008] The preparation method of the three-layer composite diaphragm is:

[0009] S1, add pyromellitic anhydride and 1, 4-p-aminophenoxy-2-phenylbenzene into NMP and stir until uniform, then add initiator, dispersant and react for 3-5h, then add capping agent and continue to react for 2-3h to obtain an intermediate, then add nanosilica and ultrasonic dispersion for 2-2.5h to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 300-350℃ for 1-1.2h under nitrogen atmosphere to obtain a polyimide base layer;

[0010] S2, disperse nanosilica in water, add N-isopropyl acrylamide and crosslinking agent, ultrasonic dispersion for 30-40min, then heat to 70-75℃, add initiator and stir for 6-8h, then centrifugal filtration and washing, freeze-drying to obtain composite particles, disperse the composite particles in ethanol, ultrasonic atomization and then spray on the surface of the polyimide base layer, the spraying thickness is 2μm, the spraying pressure is 0.3-0.5MPa, to obtain a thermal response layer;

[0011] S3, dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir for 1-2h, then centrifugal filtration and drying to obtain functional particles, then add the functional particles and dispersant into DMAC and ultrasonic dispersion for 1h, then add polyvinylidene fluoride and stir until completely dissolved to obtain a mixed solution, then use a coating machine to coat the mixed solution on the surface of the thermal response layer, the wet film thickness is 10μm, then vacuum drying at 80-85℃ for 4-6h, finally ultraviolet irradiation for 2-3min to cure, to obtain a three-layer composite separator.

[0012] Preferably, the initiator is TDI, the dispersant is sodium dodecyl sulfonate, and the capping agent is 4-(2-phenyl ethynyl) phthalic anhydride.

[0013] Preferably, the mass ratio of pyromellitic anhydride, 1, 4-p-aminophenoxy-2-phenylbenzene, NMP, initiator, dispersant, capping agent, nanosilica is 1:0.7-0.75:10-15:0.01-0.015:0.005-0.008:0.02-0.3:0.05-0.075.

[0014] Preferably, the crosslinking agent is MBA.

[0015] Preferably, the initiator is APS.

[0016] Preferably, the mass ratio of nanosilica, N-isopropyl acrylamide, crosslinking agent, initiator, ethanol is 1:1-1.1:0.005-0.006:0.01-0.02:100-120.

[0017] Preferably, the dispersant is PVP.

[0018] Preferably, the wavelength of the ultraviolet irradiation is 365nm, and the intensity is 50mW / cm 2 .

[0019] Preferably, the mass ratio of the zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, and polyvinylidene fluoride is 1:1-1.2:20-25:0.002-0.005:15-18:5-6.

[0020] Advantages of the present application:

[0021] 1. The heat response layer of the present application uses nanosilica as a rigid skeleton, and the surface is grafted with a temperature-sensitive polymer poly(N-isopropyl acrylamide), also known as PNIPAM, to form a core-shell structure. At low temperatures, the porosity is high, and the ionic conductivity is high. As the temperature rises, the PNIPAM dehydrates and shrinks, the pores rapidly close, and the ion transmission is blocked to prevent thermal runaway.

[0022] 2. The weak coordination between the hydroxyl groups on the surface of nanosilica and lithium ions in the electrolyte reduces the lithium ion migration energy barrier and improves the ionic conductivity.

[0023] 3. The polyimide base layer in the present application is composed of polyimide, providing excellent tensile strength. The heat response layer dynamically responds to temperature changes. The ion sieving layer is composed of ZIF-8 prepared from zinc nitrate hexahydrate and 2-methylimidazole, which has a small pore size and can inhibit polysulfide shuttling while adsorbing HF in the electrolyte. The three layers work together to extend the battery life and improve safety. DETAILED DESCRIPTION

[0024] The concept and technical effects of the present application will be described below in conjunction with the embodiments to fully understand the purpose, features, and effects of the present application.

[0025] In the present application, the initiator TDI is toluene diisocyanate, the crosslinking agent MBA is N,N'-methylenebisacrylamide, the initiator APS is ammonium persulfate, and the dispersant PVP is polyvinylpyrrolidone.

[0026] Example 1:

[0027] The preparation method of the three-layer composite separator described in this embodiment includes the following steps:

[0028] S1, add pyromellitic anhydride and 1, 4-p-aminophenoxy-2-phenylbenzene into NMP and stir until uniform, then add initiator, dispersant and react for 3h, then add capping agent and continue to react for 2.2h to obtain an intermediate, then add nanosilica and ultrasonic dispersion for 2.5h to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 300℃ under nitrogen atmosphere for 1.1h to obtain a polyimide base layer; the initiator is TDI, the dispersant is sodium dodecyl sulfonate, and the capping agent is 4-(2-phenylethynyl) phthalic anhydride; the mass ratio of pyromellitic anhydride, 1, 4-p-aminophenoxy-2-phenylbenzene, NMP, initiator, dispersant, capping agent, nanosilica is 1:0.72:15:0.01:0.005:0.025:0.075.

[0029] S2, disperse nanosilica in water, add N-isopropyl acrylamide and crosslinking agent, ultrasonic dispersion for 30min, then heat to 72℃, add initiator and stir for 8h, then centrifugal filtration and washing, freeze-drying to obtain composite particles, disperse the composite particles in ethanol, ultrasonic atomization, and then spray on the surface of the polyimide base layer, the spraying thickness is 2μm, the spraying pressure is 0.3MPa, to obtain a thermal response layer; the crosslinking agent is MBA, and the initiator is APS; the mass ratio of nanosilica, N-isopropyl acrylamide, crosslinking agent, initiator, ethanol is 1:1.05:0.006:0.01:110.

[0030] S3, dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir for 2h, then centrifugal filtration and drying to obtain functional particles, then add the functional particles and dispersant into DMAC and ultrasonic dispersion for 1h, then add polyvinylidene fluoride and stir until completely dissolved to obtain a mixed solution, then use a coating machine to coat the mixed solution on the surface of the thermal response layer, the wet film thickness is 10μm, then vacuum drying at 83℃ for 6h, and finally ultraviolet irradiation for 2min to cure, to obtain an ion sieve functional layer; the dispersant is PVP, the wavelength of ultraviolet irradiation is 365nm, and the intensity is 50mW / cm 2 ; the mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, polyvinylidene fluoride is 1:1.1:25:0.002:17:6.

[0031] Example 2:

[0032] The preparation method of a three-layer composite diaphragm described in this embodiment, the steps include:

[0033] S1, add pyromellitic anhydride and 1, 4-p-aminophenoxy-2-phenylbenzene into NMP and stir until uniform, then add initiator, dispersant and react for 4h, then add capping agent and continue to react for 3h to obtain an intermediate, then add nanosilica and ultrasonic dispersion for 2h to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 325℃ under nitrogen atmosphere for 1.2h to obtain a polyimide base layer; the initiator is TDI, the dispersant is sodium dodecyl sulfonate, and the capping agent is 4-(2-phenylethynyl) phthalic anhydride; the mass ratio of pyromellitic anhydride, 1, 4-p-aminophenoxy-2-phenylbenzene, NMP, initiator, dispersant, capping agent, nanosilica is 1:0.75:15:0.01:0.006:0.03:0.05.

[0034] S2, disperse nanosilica in water, add N-isopropyl acrylamide and crosslinking agent, ultrasonic dispersion for 35min, then heat to 75℃, add initiator and stir for 6h, then centrifugal filtration and washing, freeze-drying to obtain composite particles, disperse the composite particles in ethanol, ultrasonic atomization, and then spray on the surface of the polyimide base layer, the spraying thickness is 2μm, the spraying pressure is 0.4MPa, to obtain a thermal response layer; the crosslinking agent is MBA, and the initiator is APS; the mass ratio of nanosilica, N-isopropyl acrylamide, crosslinking agent, initiator, ethanol is 1:1.1:0.006:0.01:120.

[0035] S3, dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir for 1h, then centrifugal filtration and drying to obtain functional particles, then add the functional particles and dispersant into DMAC and ultrasonic dispersion for 1h, then add polyvinylidene fluoride and stir until completely dissolved to obtain a mixed solution, then use a coating machine to coat the mixed solution on the surface of the thermal response layer, the wet film thickness is 10μm, then vacuum drying at 85℃ for 4h, and finally ultraviolet irradiation for 2min to cure, to obtain an ion sieving functional layer; the dispersant is PVP, the wavelength of ultraviolet irradiation is 365nm, and the intensity is 50mW / cm 2 ; the mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, polyvinylidene fluoride is 1:1.2:20:0.003:18:5.

[0036] Example 3:

[0037] The preparation method of a three-layer composite diaphragm described in this embodiment, the steps include:

[0038] S1, add pyromellitic anhydride and 1, 4-p-aminophenoxy-2-phenylbenzene into NMP and stir until uniform, then add initiator, dispersant and react for 5h, then add capping agent and continue to react for 2h to obtain intermediate, then add nanosilica and ultrasonic dispersion for 2.2h to form uniform spinning solution, prepare nanofilm by electrospinning, and finally cure at 350℃ for 1h under nitrogen atmosphere to obtain polyimide base layer; the initiator is TDI, the dispersant is sodium dodecyl sulfonate, and the capping agent is 4-(2-phenylethynyl) phthalic anhydride; the mass ratio of pyromellitic anhydride, 1, 4-p-aminophenoxy-2-phenylbenzene, NMP, initiator, dispersant, capping agent, nanosilica is 1:0.72:15:0.01:0.006:0.03:0.05.

[0039] S2, disperse nanosilica in water, add N-isopropyl acrylamide and crosslinking agent, ultrasonic dispersion for 35min, then heat to 75℃, add initiator and stir for 6h, then centrifugal filtration and washing, freeze-drying to obtain composite particles, disperse the composite particles in ethanol, ultrasonic atomization, and then spray on the surface of the polyimide base layer, the spraying thickness is 2μm, the spraying pressure is 0.4MPa, to obtain a thermal response layer; the crosslinking agent is MBA, and the initiator is APS; the mass ratio of nanosilica, N-isopropyl acrylamide, crosslinking agent, initiator, ethanol is 1:1.1:0.005:0.015:100.

[0040] S3, dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir for 2h, then centrifugal filtration and drying to obtain functional particles, then add the functional particles and dispersant into DMAC and ultrasonic dispersion for 1h, then add polyvinylidene fluoride and stir until completely dissolved to obtain a mixed solution, then use a coating machine to coat the mixed solution on the surface of the thermal response layer, the wet film thickness is 10μm, then vacuum drying at 80℃ for 5h, and finally ultraviolet irradiation for 3min to cure, to obtain an ion sieve functional layer; the dispersant is PVP, the wavelength of ultraviolet irradiation is 365nm, and the intensity is 50mW / cm 2 ; the mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, polyvinylidene fluoride is 1:1:22:0.005:15:5.5.

[0041] Comparative Example 1:

[0042] The difference between this comparative example and Example 1 is only that the polyimide base layer is not prepared, and the rest of the raw materials and steps are the same as Example 1.

[0043] Comparative Example 2:

[0044] The difference between this comparative example and Example 1 is only that the thermal response layer is not prepared, and the rest of the raw materials and steps are the same as Example 1.

[0045] Comparative Example 3:

[0046] The present comparative example differs from Example 1 only in that no ion sieve separation functional layer is prepared, and the remaining raw materials and steps are the same as Example 1.

[0047] Performance test:

[0048] The separators of Examples 1-3 and Comparative Examples 1-3 were tested for mechanical properties, thermal shrinkage, and ion conductivity, and the specific test methods are as follows:

[0049] Mechanical properties: the tensile strength and puncture strength of the separator were tested using an electronic universal testing machine;

[0050] Porosity: the porosity at room temperature and 80°C was measured using a Gurley air permeability tester;

[0051] Ion conductivity: the electrochemical impedance curve obtained using an electrochemical workstation was used to calculate the conductivity according to the formula σ = I / RA, where I is the thickness of the separator, A is the area, and R is the impedance obtained by testing.

[0052] Table 1. Performance test results

[0053]

[0054] As can be seen from the above table, the tensile strength of Example 1 is higher than that of Comparative Example 1, because a polyimide base layer is prepared in Example 1, and a three-dimensional honeycomb structure is formed by electrospinning using polyimide, which has good heat resistance and high tensile strength. The 80°C porosity of Example 1 is lower than that of Comparative Example 2, because a thermal response layer is prepared in Example 1, which has high porosity at low temperature, and as the temperature rises, the PNIPAM shrinks by dehydration, the pores close rapidly, blocking ion transmission to prevent thermal runaway, making the battery have high safety. The ion conductivity of Example 1 is higher than that of Comparative Example 3, because an ion sieve layer is prepared in Example 1, which has a small pore size and low ion transmission rate, which can block harmful ions and small molecule substances such as polysulfides from passing through the separator, further improving the safety of the battery.

[0055] The above examples are only a part of the embodiments of the present application, not all embodiments, and other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative labor are within the scope of protection of the present application.

Claims

1. A three-layer composite diaphragm, characterized in that, It consists of three layers, which are composited from the inside out: a polyimide base layer, a thermally responsive layer, and an ion-sieving functional layer. The polyimide base layer is composed of polyimide; the thermally responsive layer is obtained by polymerization of N-isopropylacrylamide; and the ion-sieve layer is composed of zinc nitrate hexahydrate and 2-methylimidazole reacted. The three-layer composite membrane includes the following steps: S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir until homogeneous. Then add initiator and dispersant and react for 3-5 hours. Next, add end-capping agent and continue reacting for 2-3 hours to obtain an intermediate. Then add nano-silica and ultrasonically disperse for 2-2.5 hours to form a uniform spinning solution. Prepare a nanofilm by electrospinning. Finally, cure at 300-350℃ for 1-1.2 hours under nitrogen atmosphere to obtain a polyimide substrate layer. S2. Disperse nano-silica in water, add N-isopropylacrylamide and crosslinking agent, and ultrasonically disperse for 30-40 min. Then, heat to 70-75℃, add initiator and stir for 6-8 h. Then, centrifuge, filter and wash, freeze dry to obtain composite particles. Disperse the composite particles in ethanol, ultrasonically atomize and spray them onto the surface of polyimide substrate with a coating thickness of 2 μm and a spraying pressure of 0.3-0.5 MPa to obtain a thermally responsive layer. S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir and react for 1-2 hours, then centrifuge, wash and dry to obtain functional particles. Then add the functional particles and dispersant to DMAC and ultrasonically disperse for 1 hour. Then add polyvinylidene fluoride and stir until completely dissolved to obtain a mixture. Then use a coating machine to coat the mixture onto the surface of the thermally responsive layer with a wet film thickness of 10 μm. Then vacuum dry at 80-85℃ for 4-6 hours, and finally cure by UV irradiation for 2-3 minutes to obtain a three-layer composite membrane.

2. The three-layer composite diaphragm according to claim 1, characterized in that, The initiator is TDI, the dispersant is sodium dodecyl sulfonate, and the end-capping agent is 4-(2-phenylethynyl)phthalic anhydride.

3. The three-layer composite diaphragm according to claim 1, characterized in that, The mass ratio of the pyromellitic anhydride, 1,4-p-aminophenoxy-2-phenylbenzene, NMP, initiator, dispersant, capping agent, and nano silica is 1:0.7-0.75:10-15:0.01-0.015:0.005-0.008:0.02-0.3:0.05-0.

075.

4. The three-layer composite diaphragm according to claim 1, characterized in that, The crosslinking agent is MBA.

5. A three-layer composite diaphragm according to claim 1, characterized in that, The initiator is APS.

6. The three-layer composite diaphragm according to claim 1, characterized in that, The mass ratio of the nano-silica, N-isopropylacrylamide, crosslinking agent, initiator, and ethanol is 1:1-1.1:0.005-0.006:0.01-0.02:100-120.

7. The three-layer composite diaphragm according to claim 1, characterized in that, The dispersant is PVP.

8. A three-layer composite diaphragm according to claim 1, characterized in that, The ultraviolet irradiation has a wavelength of 365nm and an intensity of 50mW / cm².

9. A three-layer composite diaphragm according to claim 1, characterized in that, The mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, and polyvinylidene fluoride is 1:1-1.2:20-25:0.002-0.005:15-18:5-6.

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