Three-layer composite diaphragm and preparation method thereof

Abstract

The invention relates to the technical field of batteries, and discloses a three-layer composite diaphragm and a preparation method thereof, and the three-layer composite diaphragm comprises three layers: a polyimide substrate layer, a thermal response layer and an ion screening function layer which are sequentially compounded from inside to outside. According to the thermal response layer, nano silicon dioxide serves as a rigid framework, a temperature-sensitive polymer poly (N-isopropylacrylamide) is grafted on the surface, a core-shell structure is formed, the porosity and the ionic conductivity are high at the low temperature, PNIPAM is dehydrated and shrunk along with temperature rise, pores are rapidly closed, ion transmission is blocked, and thermal runaway is prevented. In addition, the polyimide substrate layer provides excellent mechanical tensile strength, the ion sieve layer inhibits shuttling of polysulfide and adsorbs HF in electrolyte, and the three layers are compounded and act together, so that the service life of the battery is prolonged, and the safety is improved.

Description

Technical Field

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

[0002] The battery separator is a key component in lithium-ion batteries. Its main function is to physically separate the positive and negative electrodes of the battery to prevent short circuits, while allowing lithium ions to pass freely to complete the charge and discharge cycle. The functional properties of the battery separator directly affect the battery's energy density, cycle life, and safety. For example, ceramic coatings can enhance resistance to dendrite penetration. With the development of solid-state batteries, new separators tend to be ultra-thin, such as less than 5μm, and integrate electrolyte functions. Smart separators can also monitor internal pressure or temperature changes in the battery in real time, providing guarantees for the safe operation of high-energy-density batteries.

[0003] Currently, common diaphragms are mainly made of PE and PP, which have a low thermal deformation temperature. When the temperature is too high, the diaphragm will shrink severely, which can easily lead to contact between the positive and negative poles of the battery and cause a short circuit, which in turn causes thermal runaway of the battery. 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 with a high-temperature fluorine-containing liquid crystal polymer and polyvinylidene fluoride, as well as its preparation method and application. The orderly arrangement of the liquid crystal polymer molecular chains makes the modified diaphragm have higher mechanical strength and toughness, and can withstand greater stress during the battery charge and discharge process; and the presence of fluorine-containing groups improves the heat resistance of the material, while maintaining an appropriate porosity to ensure the smooth conduction of lithium ions, thereby ensuring the safety and life of the battery. Although the diaphragm prepared by this method has a higher heat resistance, it still cannot avoid the problem of the diaphragm shrinking and deforming at high temperatures, causing short circuit and runaway of the battery. Summary of the Invention

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

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A three-layer composite diaphragm, comprising three layers laminated sequentially from the inside to the outside: a polyimide base layer, a thermal response layer, and an ion screening functional layer;

[0007] The polyimide base layer is composed of polyimide; the thermal response layer is obtained by polymerization of N-isopropylacrylamide; and the ion screening layer is formed by the reaction of zinc nitrate hexahydrate and 2-methylimidazole.

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

[0009] S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir evenly, then add an initiator and a dispersant to react for 3-5 hours, then add a capping agent and continue to react 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, and finally cure at 300-350° C. in a nitrogen atmosphere for 1-1.2 hours to obtain a polyimide base layer;

[0010] S2. Dispersing nano-silica in water, adding N-isopropylacrylamide and a cross-linking agent, and ultrasonically dispersing for 30-40 minutes, then heating to 70-75°C, adding an initiator and stirring to react for 6-8 hours, then centrifugally filtering and washing, and freeze-drying to obtain composite particles, dispersing the composite particles in ethanol, ultrasonically atomizing, and spraying them on the surface of the polyimide base layer at a spraying thickness of 2 μm and a spraying pressure of 0.3-0.5 MPa to obtain a thermal responsive layer;

[0011] S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir to 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 mixed solution. Then use a coater to coat the mixed solution on the surface of the thermal response layer with a wet film thickness of 10 μm. Then vacuum dry at 80-85°C for 4-6 hours, and finally cure under ultraviolet irradiation for 2-3 minutes to obtain a three-layer composite membrane.

[0012] Preferably, the initiator is TDI, the dispersant is sodium dodecylsulfonate, and the end-capping agent is 4-(2-phenylethynyl)phthalic anhydride.

[0013] Preferably, 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.

[0014] Preferably, the cross-linking agent is MBA.

[0015] Preferably, the initiator is APS.

[0016] Preferably, the mass ratio of the nano-silica, N-isopropylacrylamide, cross-linking agent, initiator and 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 365 nm and the intensity is 50 mW / cm 2 .

[0019] Preferably, 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.

[0020] Beneficial effects of the present invention:

[0021] 1. The thermal response layer of the present invention uses nano-silica as a rigid skeleton and grafts a thermosensitive polymer poly (N-isopropylacrylamide), also called PNIPAM, on the surface to form a core-shell structure. It has high porosity and high ionic conductivity at low temperatures. As the temperature rises, PNIPAM dehydrates and shrinks, the pores close rapidly, and ion transmission is blocked to prevent thermal runaway.

[0022] 2. The hydroxyl groups on the surface of nano-silica form a weak coordination effect with the lithium ions in the electrolyte, reducing the energy barrier for lithium ion migration and improving ionic conductivity.

[0023] 3. The polyimide base layer in the present invention is composed of polyimide, which provides excellent tensile strength; the thermal response layer dynamically responds to temperature changes; the ion screening layer is composed of ZIF-8 prepared from zinc nitrate hexahydrate and 2-methylimidazole to form a skeleton, which has a small pore size and can inhibit polysulfide shuttle and adsorb HF in the electrolyte; the three layers work together to extend battery life and improve safety. DETAILED DESCRIPTION

[0024] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments so as to fully understand the purpose, characteristics and effects of the present invention.

[0025] In the present invention, 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 a three-layer composite diaphragm described in this embodiment comprises the following steps:

[0028] S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir evenly, then add an initiator and a dispersant to react for 3 hours, then add a capping agent and continue to react for 2.2 hours to obtain an intermediate, then add nano-silica and ultrasonically disperse for 2.5 hours to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 300°C in a nitrogen atmosphere for 1.1 hours to obtain a polyimide base layer; the initiator is TDI, the dispersant is sodium dodecylsulfonate, 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, and nano-silica is 1:0.72:15:0.01:0.005:0.025:0.075.

[0029] S2. Disperse nano-silica in water, add N-isopropylacrylamide and a cross-linking agent, and ultrasonically disperse for 30 minutes. Then heat to 72°C, add an initiator and stir to react for 8 hours, then centrifuge, filter, wash, and freeze-dry to obtain composite particles. Disperse the composite particles in ethanol, ultrasonically atomize, and spray them on the surface of the polyimide base layer with a spraying thickness of 2 μm and a spraying pressure of 0.3 MPa to obtain a thermal response layer. The cross-linking agent is MBA and the initiator is APS. The mass ratio of the nano-silica, N-isopropylacrylamide, cross-linking agent, initiator, and ethanol is 1:1.05:0.006:0.01:110.

[0030] S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir and react for 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 mixed solution. Then use a coater to coat the mixed solution on the surface of the thermal response layer with a wet film thickness of 10 μm. Then vacuum dry at 83°C for 6 hours, and finally cure under ultraviolet irradiation for 2 minutes to obtain an ion screening functional layer. The dispersant is PVP, and the wavelength of ultraviolet irradiation is 365 nm and the intensity is 50 mW / cm 2 The mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, and 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 comprises the following steps:

[0033] S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir evenly, then add an initiator and a dispersant to react for 4 hours, then add a capping agent and continue to react for 3 hours to obtain an intermediate, then add nano-silica and ultrasonically disperse for 2 hours to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 325°C in a nitrogen atmosphere for 1.2 hours to obtain a polyimide base layer; the initiator is TDI, the dispersant is sodium dodecylsulfonate, 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, and nano-silica is 1:0.75:15:0.01:0.006:0.03:0.05.

[0034] S2. Disperse nano-silica in water, add N-isopropylacrylamide and a cross-linking agent, and ultrasonically disperse for 35 minutes. Then, heat to 75°C, add an initiator and stir to react for 6 hours, then centrifuge, filter, wash, and freeze-dry to obtain composite particles. Disperse the composite particles in ethanol, ultrasonically atomize, and spray them on the surface of the polyimide base layer with a spraying thickness of 2 μm and a spraying pressure of 0.4 MPa to obtain a thermal response layer. The cross-linking agent is MBA and the initiator is APS. The mass ratio of the nano-silica, N-isopropylacrylamide, cross-linking agent, initiator, and ethanol is 1:1.1:0.006:0.01:120.

[0035] S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir and react for 1 hour, 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 mixed solution, then use a coater to coat the mixed solution on the surface of the thermal response layer with a wet film thickness of 10 μm, then vacuum dry at 85°C for 4 hours, and finally cure under ultraviolet irradiation for 2 minutes to obtain an ion screening functional layer; the dispersant is PVP, the wavelength of ultraviolet irradiation is 365 nm, and the intensity is 50 mW / cm 2 The mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, and 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 comprises the following steps:

[0038] S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir evenly, then add an initiator and a dispersant to react for 5 hours, then add a capping agent and continue to react for 2 hours to obtain an intermediate, then add nano-silica and ultrasonically disperse for 2.2 hours to form a uniform spinning solution, prepare a nanofilm by electrospinning, and finally cure at 350°C in a nitrogen atmosphere for 1 hour to obtain a polyimide base layer; the initiator is TDI, the dispersant is sodium dodecylsulfonate, 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, and nano-silica is 1:0.72:15:0.01:0.006:0.03:0.05.

[0039] S2. Disperse nano-silica in water, add N-isopropylacrylamide and a cross-linking agent, and ultrasonically disperse for 35 minutes. Then, heat to 75°C, add an initiator and stir to react for 6 hours, then centrifuge, filter, wash, and freeze-dry to obtain composite particles. Disperse the composite particles in ethanol, ultrasonically atomize, and spray them on the surface of the polyimide base layer with a spraying thickness of 2 μm and a spraying pressure of 0.4 MPa to obtain a thermal response layer. The cross-linking agent is MBA and the initiator is APS. The mass ratio of the nano-silica, N-isopropylacrylamide, cross-linking agent, initiator, and ethanol is 1:1.1:0.005:0.015:100.

[0040] S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir and react for 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 mixed solution. Then use a coater to coat the mixed solution on the surface of the thermal response layer with a wet film thickness of 10 μm. Then vacuum dry at 80°C for 5 hours, and finally cure under ultraviolet irradiation for 3 minutes to obtain an ion screening functional layer. The dispersant is PVP, and the wavelength of ultraviolet irradiation is 365 nm and the intensity is 50 mW / cm 2 The mass ratio of zinc nitrate hexahydrate, 2-methylimidazole, methanol, dispersant, DMAC, and polyvinylidene fluoride is 1:1:22:0.005:15:5.5.

[0041] Comparative Example 1:

[0042] The only difference between this comparative example and Example 1 is that no polyimide base layer is prepared, and the remaining raw materials and steps are the same as those in Example 1.

[0043] Comparative Example 2:

[0044] The only difference between this comparative example and Example 1 is that no thermal response layer is prepared, and the remaining raw materials and steps are the same as those in Example 1.

[0045] Comparative Example 3:

[0046] The only difference between this comparative example and Example 1 is that no ion screening functional layer is prepared, and the remaining raw materials and steps are the same as those in Example 1.

[0047] Performance testing:

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

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

[0050] Porosity: Gurley permeability tester was used to measure the porosity at room temperature and 80°C.

[0051] Ionic conductivity: The electrochemical impedance curve is obtained by electrochemical workstation testing. The conductivity is calculated according to the formula σ = I / RA, where the thickness of the diaphragm is I, the area is A, and R is the measured impedance.

[0052] Table 1. Performance test results

[0053]

[0054] As can be seen from the above table, Example 1 has a higher tensile strength than Comparative Example 1. This is because a polyimide base layer is prepared in Example 1, and polyimide is used to form a three-dimensional honeycomb structure by electrospinning, which has good heat resistance and high tensile strength. Example 1 has a lower porosity at 80°C than Comparative Example 2. This is because a thermal response layer is prepared in Example 1, and the porosity is high at low temperatures. As the temperature rises, PNIPAM dehydrates and shrinks, and the pores close rapidly, blocking ion transmission to prevent thermal runaway, so that the battery has higher safety. Example 1 has a higher ionic conductivity than Comparative Example 3. This is because an ion screening layer is prepared in Example 1, which has a small pore size and a low ion pass rate. It can block harmful ions and small molecules such as polysulfides from passing through the diaphragm, further improving battery safety.

[0055] The above embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

Claims

1. A three-layer composite diaphragm, characterized in that: It includes three layers compounded from the inside to the outside: a polyimide base layer, a thermal response layer, and an ion screening functional layer; The polyimide base layer is composed of polyimide; the thermal response layer is obtained by polymerization of N-isopropylacrylamide; and the ion screening layer is formed by the reaction of zinc nitrate hexahydrate and 2-methylimidazole.

2. The method for preparing a three-layer composite diaphragm according to claim 1, characterized in that: The preparation method is: S1. Add pyromellitic anhydride and 1,4-p-aminophenoxy-2-phenylbenzene to NMP and stir evenly, then add an initiator and a dispersant to react for 3-5 hours, then add a capping agent and continue to react 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, and finally cure at 300-350° C. in a nitrogen atmosphere for 1-1.2 hours to obtain a polyimide base layer; S2. Dispersing nano-silica in water, adding N-isopropylacrylamide and a cross-linking agent, and ultrasonically dispersing for 30-40 minutes, then heating to 70-75°C, adding an initiator and stirring to react for 6-8 hours, then centrifugally filtering and washing, and freeze-drying to obtain composite particles, dispersing the composite particles in ethanol, ultrasonically atomizing, and spraying them on the surface of the polyimide base layer at a spraying thickness of 2 μm and a spraying pressure of 0.3-0.5 MPa to obtain a thermal responsive layer; S3. Dissolve zinc nitrate hexahydrate and 2-methylimidazole in methanol, stir to 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 mixed solution. Then use a coater to coat the mixed solution on the surface of the thermal response layer with a wet film thickness of 10 μm. Then vacuum dry at 80-85°C for 4-6 hours, and finally cure under ultraviolet irradiation for 2-3 minutes to obtain a three-layer composite membrane.

3. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The initiator is TDI, the dispersant is sodium dodecylsulfonate, and the end-capping agent is 4-(2-phenylethynyl)phthalic anhydride.

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

075.

5. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The cross-linking agent is MBA.

6. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The initiator is APS.

7. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The mass ratio of the nano-silica, N-isopropylacrylamide, cross-linking agent, initiator and ethanol is 1:1-1.1:0.005-0.006:0.01-0.02:100-120.

8. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The dispersant is PVP.

9. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: The wavelength of the ultraviolet irradiation is 365 nm and the intensity is 50 mW / cm 2 .

10. The method for preparing a three-layer composite diaphragm according to claim 2, characterized in that: 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.

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