High-strength PI nanofiber porous membrane and preparation method thereof

Abstract

The invention discloses a high-strength PI nanofiber porous membrane and a preparation method thereof.The preparation method of the high-strength PI nanofiber porous membrane comprises the following steps that polyvinylidene fluoride and an acrylic acid homopolymer are added into a flask according to the proportion, dimethylformamide is added, and the mixture is stirred and dissolved; the preparation method disclosed by the invention has the beneficial effects that the polyimide-based nanofiber porous membrane is prepared by an electrostatic spinning technology and is used as a novel safe battery diaphragm; compared with a commercialized polyolefin diaphragm prepared by a traditional dry or wet pore-forming process, the composite diaphragm has better comprehensive properties such as high porosity, electrolyte wettability, wrinkle resistance, flexibility, high temperature resistance, chemical corrosion resistance and the like, the use safety of a lithium ion battery is greatly improved, and the composite diaphragm has excellent electrochemical performance; benzimidazole with a rigid structure is added, so that hydrogen bonds exist among imidized fiber molecular chains, the interaction force among the fiber molecular chains can be increased, and the strength of the PI nanofiber porous membrane is further improved.

Description

Technical Field

[0001] The invention relates to the technical field of PI nanofiber porous membranes, in particular to a high-strength PI nanofiber porous membrane and a preparation method thereof. Background Art

[0002] With the rapid development of nanomaterial technology, nanofiber technology has become the forefront and research hotspot of fiber science. Methods for preparing nanofibers include stretching, template polymerization, phase separation, self-organization and electrospinning, among which electrospinning is the most common and important method for preparing continuous ultrafine fibers and non-woven fabrics. The non-woven membrane material prepared by electrospinning has the characteristics of low density, large specific surface area, high porosity and uniform pores. Therefore, this type of membrane material has good filtration, barrier and thermal insulation properties. These properties of nanofibers can be used to make low dielectric materials, diaphragm materials, adsorption materials, filtration materials, composite reinforcement materials, thin thermal insulation materials, protective materials, etc., which are used in circuit boards of electronic products, diaphragms of capacitors and batteries, filtration of submicron particles and multifunctional protection.

[0003] Diaphragms prepared by dry or wet methods have been commercialized due to their good chemical stability, wide sources of raw materials and low preparation costs. Polyolefin diaphragms prepared by traditional dry and wet pore-forming processes have low porosity, and the material itself is non-polar, resulting in poor compatibility and wettability with polar organic electrolytes, resulting in high ion conduction resistance in the interface layer between the diaphragm and the electrode, which limits the electrochemical performance of the final battery. To this end, the present application proposes a high-strength PI nanofiber porous membrane and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a high-strength PI nanofiber porous membrane and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a high-strength PI nanofiber porous membrane, wherein the PI nanofiber porous membrane has a pore size distribution of 30-550nm, a porosity of ≥70%, a tensile strength of ≥75MPa, and a BET specific surface area of ​​153-175m 2 / g, pore volume is 0.44-0.58cm 3 / g, thermal shrinkage ≤0.27%, melting temperature ≥200.

[0006] The method for preparing a high-strength PI nanofiber porous membrane comprises the following steps: S1, adding polyvinylidene fluoride and acrylic acid homopolymer into a flask according to the ratio, and adding dimethylformamide, stirring and dissolving them; S2, adding benzimidazole in batches under low temperature conditions, adding inert gas and performing mechanical stirring reaction to obtain a polyamic acid solution for standby use; S3, using an electrospinning machine to spray the polyamic acid solution in a high voltage electric field to obtain electrospinning with a diameter of nanometers, and according to the set electrospinning parameters and environmental conditions, the nano-electrospinning is made into a blended fiber membrane, and dried for standby use; S4. The blended fiber membrane is thermally imidized in a vacuum tube furnace using a gradient heating method, and a high-strength PI nanofiber porous membrane can be obtained after cooling.

[0007] Preferably, the time interval for adding benzimidazole in step S2 is 30 minutes.

[0008] Preferably, the inert gas in step S2 is nitrogen.

[0009] Preferably, the reaction time in step S2 is 4-8 hours, and the reaction temperature is 5-10°C.

[0010] Preferably, the electrostatic prevention parameters in step S3 are: the spinning distance is set to 12-15 cm, the syringe solution is 10 ml, the spinning speed is 1.8-2.7 ml / h, the spinning time is 3-5 h, the spinning positive voltage is +10.0 KV, and the spinning negative voltage is -1.0 KV.

[0011] Preferably, the thermal imidization in step S4 is carried out by gradient heating under vacuum or inert gas conditions, from room temperature at a heating rate of 5-20°C / min, and maintained at 180-250°C for 5-30min and at 300-360°C for 5-30min.

[0012] Preferably, the viscosity of the polyamic acid solution in step S2 is 1.7-9 Pa·s.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: a polyimide-based nanofiber porous membrane is prepared by electrospinning technology. As a new type of safe battery separator, it has better comprehensive properties such as high porosity and electrolyte wettability, wrinkle resistance and flexibility, high temperature resistance and chemical corrosion resistance than commercial polyolefin separators prepared by traditional dry or wet pore-making processes, which greatly improves the safety of lithium-ion batteries and has excellent electrochemical performance. The addition of benzimidazole with a rigid structure allows hydrogen bonds to exist between the fiber molecular chains after imidization, which can increase the interaction force between the fiber molecular chains, thereby improving the strength of the PI nanofiber porous membrane. DETAILED DESCRIPTION

[0014] The present invention is described in detail below, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] The present invention is described in detail below, and the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0016] The present invention provides a technical solution: A high-strength PI nanofiber porous membrane, wherein the PI nanofiber porous membrane has a pore size distribution of 30-550nm, a porosity of ≥70%, a tensile strength of ≥75MPa, and a BET specific surface area of ​​153-175m 2 / g, pore volume is 0.44-0.58cm 3 / g, thermal shrinkage ≤0.27%, melting temperature ≥200.

[0017] The method for preparing a high-strength PI nanofiber porous membrane comprises the following steps: S1, adding polyvinylidene fluoride and acrylic acid homopolymer into a flask according to the ratio, and adding dimethylformamide, stirring and dissolving them; S2, adding benzimidazole in batches under low temperature conditions, adding inert gas and performing mechanical stirring reaction to obtain a polyamic acid solution for standby use; S3, using an electrospinning machine to spray the polyamic acid solution in a high voltage electric field to obtain electrospinning with a diameter of nanometers, and according to the set electrospinning parameters and environmental conditions, the nano-electrospinning is made into a blended fiber membrane, and dried for standby use; S4. The blended fiber membrane is thermally imidized in a vacuum tube furnace using a gradient heating method, and a high-strength PI nanofiber porous membrane can be obtained after cooling.

[0018] Wherein, the time interval for adding benzimidazole in step S2 is 30 minutes.

[0019] Wherein, the inert gas in step S2 is nitrogen.

[0020] Wherein, the reaction time in step S2 is 4-8 hours, and the reaction temperature is 5-10°C.

[0021] Among them, the electrostatic prevention parameters in step S3 are: the spinning distance is set to 12-15 cm, the syringe solution is 10 ml, the spinning speed is 1.8-2.7 ml / h, the spinning time is 3-5 h, the spinning positive voltage is +10.0 KV, and the spinning negative voltage is -1.0 KV.

[0022] Wherein, in step S4, the thermal imidization is carried out by gradient heating under vacuum or inert gas conditions, from room temperature at a heating rate of 5-20°C / min, and maintained at 180-250°C for 5-30min, and maintained at 300-360°C for 5-30min.

[0023] Wherein, the viscosity of the polyamic acid solution in step S2 is 1.7-9 Pa·s.

[0024] Embodiment 1:

[0025] According to the molar ratio of polyvinylidene fluoride: acrylic acid homopolymer: dimethylformamide = 3:5:8, polyvinylidene fluoride and acrylic acid homopolymer are added to a flask according to the ratio, and dimethylformamide is added, and the mixture is stirred and dissolved. Benzimidazole is added three times at intervals of 30 minutes under low temperature conditions. After adding nitrogen gas, the mixture is mechanically stirred and reacted at 5°C for 8 hours to obtain a polyamic acid solution with a viscosity of 2.3 Pa·s. The polyamic acid solution is sprayed out in a high-voltage electric field using an electrospinning machine to obtain electrospun fibers with a diameter of nanometers. The spinning distance is set to 12 cm, the syringe solution is 10 ml, and the spinning speed is set to 2.30 μm. The electrospinning rate was 1.8 ml / h, the spinning time was 5 h, the spinning positive voltage was +10.0 KV, the spinning negative voltage was -1.0 KV, and the nano-electrospinning was made into a blended fiber membrane according to the set electrospinning parameters, and then dried. The blended fiber membrane was thermally imidized in a vacuum tube furnace using a gradient heating method, and the heating rate was 5 ° C / min, and it was kept at 180 ° C for 30 min, and kept at 300 ° C for 30 min. After cooling to 70 ° C, a high-strength PI nanofiber porous membrane was obtained; the obtained polyimide nanofiber porous membrane has good heat resistance and tensile resistance, and the BET specific surface area is 153 m 2 / g, pore volume is 0.44cm 3 / g, the porosity of the fiber porous membrane is 73%, the average pore size is 78nm; the tensile strength of the fiber porous membrane is 75MPa, the fiber diameter is 180nm, and the shrinkage rate is 0.18% when kept at 180℃ for 3 hours.

[0026] Embodiment 2:

[0027] According to the molar ratio of polyvinylidene fluoride: acrylic acid homopolymer: dimethylformamide = 1:7:11, polyvinylidene fluoride and acrylic acid homopolymer are added to a flask according to the ratio, and dimethylformamide is added, and the mixture is stirred and dissolved. Benzimidazole is added three times at intervals of 30 minutes under low temperature conditions. After adding nitrogen gas, the mixture is mechanically stirred and reacted at 8°C for 6 hours to obtain a polyamic acid solution with a viscosity of 5.3 Pa·s. The polyamic acid solution is sprayed out in a high-voltage electric field using an electrospinning machine to obtain electrospun fibers with a diameter of nanometers. The spinning distance is set to 14 cm, the syringe solution is 10 ml, and the spinning speed is set to 200 nm. The spinning rate was 1.8 ml / h, the spinning time was 4 h, the spinning positive voltage was +10.0 KV, the spinning negative voltage was -1.0 KV, and the nano-electrospinning was made into a blended fiber membrane according to the set electrospinning parameters, and then dried. The blended fiber membrane was thermally imidized in a vacuum tube furnace using a gradient heating method, and the heating rate was 15 ° C / min, and it was kept at 220 ° C for 25 min, and kept at 330 ° C for 25 min. After cooling to 70 ° C, a high-strength PI nanofiber porous membrane was obtained; the obtained polyimide nanofiber porous membrane had good heat resistance and tensile strength, and the BET specific surface area was 153 m 2 / g, pore volume is 0.44cm 3 / g, the porosity of the fiber porous membrane is 75.3%, the average pore size is 182nm; the tensile strength of the fiber porous membrane is 93MPa, the fiber diameter is 203nm, and the shrinkage rate is 0.22% when kept at 220℃ for 3 hours.

[0028] Embodiment 3:

[0029] According to the molar ratio of polyvinylidene fluoride: acrylic acid homopolymer: dimethylformamide = 2:6:12, polyvinylidene fluoride and acrylic acid homopolymer are added to a flask according to the ratio, and dimethylformamide is added, and the mixture is stirred and dissolved. Benzimidazole is added three times at intervals of 30 minutes under low temperature conditions. After adding nitrogen gas, the mixture is mechanically stirred and reacted at 10°C for 4 hours to obtain a polyamic acid solution with a viscosity of 7.9 Pa·s. The polyamic acid solution is sprayed out in a high-voltage electric field using an electrospinning machine to obtain electrospun fibers with a diameter of nanometers. The spinning distance is set to 15 cm, the syringe solution is 10 ml, and the spinning The spinning speed was 2.7 ml / h, the spinning time was 3 h, the spinning positive voltage was +10.0 KV, the spinning negative voltage was -1.0 KV, and the nano-electrospinning was made into a blended fiber membrane according to the set electrospinning parameters, and then dried. The blended fiber membrane was thermally imidized in a vacuum tube furnace using a gradient heating method, with a heating rate of 5 ° C / min, and kept at 180 ° C for 30 min, kept at 300 ° C for 30 min, and cooled to 70 ° C to obtain a high-strength PI nanofiber porous membrane; the obtained polyimide nanofiber porous membrane has good heat resistance and tensile resistance, and the BET specific surface area is 165 m2 / g, pore volume is 0.51cm 3 / g, the porosity of the fiber porous membrane is 81%, and the average pore size is 327nm; the tensile strength of the fiber porous membrane is 117MPa, the fiber diameter is 253nm, and the shrinkage rate is 0.25% when kept at 220℃ for 3 hours.

[0030] The above description enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-strength PI nanofiber porous membrane, characterized in that: The PI nanofiber porous membrane has a pore size distribution of 30-550 nm, a porosity of ≥70%, a tensile strength of ≥75 MPa, and a BET specific surface area of ​​153-175 m 2 / g, pore volume is 0.44-0.58cm 3 / g, thermal shrinkage ≤0.27%, melting temperature ≥200℃.

2. A method for preparing a high-strength PI nanofiber porous membrane, characterized in that: The following steps are involved: S1. Add polyvinylidene fluoride and acrylic acid homopolymer into a flask according to the ratio, and add dimethylformamide, and stir to dissolve them; S2, adding benzimidazole in batches under low temperature conditions, adding inert gas and performing mechanical stirring reaction to obtain a polyamic acid solution for standby use; S3, using an electrospinning machine to spray the polyamic acid solution in a high voltage electric field to obtain electrospinning with a diameter of nanometers, and according to the set electrospinning parameters and environmental conditions, the nano-electrospinning is made into a blended fiber membrane, and dried for standby use; S4. The blended fiber membrane is thermally imidized in a vacuum tube furnace using a gradient heating method, and a high-strength PI nanofiber porous membrane can be obtained after cooling.

3. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: The time interval for adding benzimidazole in step S2 is 30 minutes.

4. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: The inert gas in step S2 is nitrogen.

5. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: The reaction time in step S2 is 4-8 hours, and the reaction temperature is 5-10°C.

6. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: The electrostatic prevention parameters in step S3 are: the spinning distance is set to 12-15 cm, the syringe solution is 10 ml, the spinning speed is 1.8-2.7 ml / h, the spinning time is 3-5 h, the spinning positive voltage is +10.0 KV, and the spinning negative voltage is -1.0 KV.

7. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: In the step S4, the thermal imidization is carried out by gradient heating under vacuum or inert gas conditions, from room temperature at a heating rate of 5-20°C / min, and maintained at 180-250°C for 5-30min and at 300-360°C for 5-30min.

8. The method for preparing a high-strength PI nanofiber porous membrane according to claim 2, characterized in that: The viscosity of the polyamic acid solution in step S2 is 1.7-9 Pa·s.