阅读说明：本技术 一种具有热闭孔功能的聚酰亚胺隔膜及其制备方法 (Polyimide diaphragm with thermal pore-closing function and preparation method thereof ) 是由 齐胜利 李腾飞 王亚丽 王芮晗 田国峰 武德珍 于 2021-09-08 设计创作，主要内容包括：一种具有热闭孔功能的聚酰亚胺隔膜及其制备方法。其制备方法为：合成热固性聚酰亚胺前驱体聚酰胺酸溶液置于外层针头推进器中,将热塑性聚酰亚胺粉体溶解在有机溶剂中,置于内层针头推进器中并进行同轴电纺,最后将所得纤维膜膜进行热酰亚胺化处理,得到具有热闭孔功能的聚酰亚胺电池隔膜。所述具有热闭孔功能的聚酰亚胺隔膜为同轴复合纳米纤维结构,壳层为热固性聚酰亚胺,芯层为热塑性聚酰亚胺。本发明所制备的具有热闭孔功能的电纺复合隔膜,闭孔后膜收缩小于2％,能够显著提高电池安全性,在电池领域具有很好额应用前景电池安全性方面显示出巨大的应用前景。(A polyimide diaphragm with a thermal pore-closing function and a preparation method thereof. The preparation method comprises the following steps: and (3) putting the polyamide acid solution for synthesizing the thermosetting polyimide precursor into an outer-layer needle propeller, dissolving thermoplastic polyimide powder into an organic solvent, putting the organic solvent into an inner-layer needle propeller, carrying out coaxial electrospinning, and finally carrying out thermal imidization treatment on the obtained fiber membrane to obtain the polyimide battery diaphragm with the thermal hole-closing function. The polyimide diaphragm with the thermal pore-closing function is of a coaxial composite nanofiber structure, the shell layer is made of thermosetting polyimide, and the core layer is made of thermoplastic polyimide. The prepared electro-spinning composite diaphragm with the hot hole closing function has the advantages that the shrinkage of the diaphragm after hole closing is less than 2%, the safety of the battery can be obviously improved, and the electro-spinning composite diaphragm has good application prospect in the field of batteries and shows a huge application prospect in the aspect of battery safety.)

1. A polyimide diaphragm with a thermal pore-closing function is characterized in that the diaphragm is a nanofiber porous membrane, wherein nanofibers are in a shell-core structure, a shell layer is made of thermosetting polyimide and has a thickness of 50-600nm, and a core layer is made of thermoplastic polyimide and has a diameter of 50-300 nm; the thickness of the diaphragm is 3-30 μm.

2. The method for preparing a polyimide separator having a thermal shut-off function according to claim 1, comprising the steps of:

a, synthesizing a thermosetting polyimide precursor polyamic acid solution with the solid content of 6-35 percent;

b: dissolving thermoplastic polyimide powder in an organic solvent to prepare a thermoplastic polyimide solution with solid content of 8-50%;

c: adding the polyamic acid solution of the thermosetting polyimide precursor prepared in the step A into an outer needle injector of a coaxial electrostatic spinning device, adding the thermoplastic polyimide solution obtained in the step B into an inner needle injector of the coaxial electrostatic spinning device for electrostatic spinning, wherein the inner needle has the aperture of 0.3-0.8mm, the outer needle has the aperture of 0.5-1.8mm, the spinning voltage is 15-50kV, the receiving distance is 16-30cm, and the humidity is 20-50%;

d: and C, performing heating thermal imidization treatment on the nano fiber membrane with the shell-core structure prepared in the step C, heating the nano fiber membrane from room temperature to 350 ℃, and preserving the heat for 15min-4h to obtain the polyimide battery diaphragm with the thermal hole-closing function.

3. The method for preparing a polyimide separator having a thermal cell shutdown function according to claim 2, wherein the thermosetting polyimide in the step a may be one or more of a pyromellitic dianhydride/4, 4 '-diaminodiphenyl ether system, a 3,3',4,4 '-benzophenonetetracarboxylic dianhydride/4, 4' -diaminodiphenyl ether system, a 3,3',4,4' -biphenyltetracarboxylic dianhydride/4, 4 '-diaminodiphenyl ether system, and a hexafluoro dianhydride/4, 4' -diaminodiphenyl ether system.

4. The method for preparing a polyimide separator having a thermal shut-off function according to claim 2, wherein the thermoplastic polyimide in step A is polyetherimide, P84 copolyimide, 9-bis (4-aminophenyl) -2, 2-bis [4- (4-aminophenoxy) phenyl ] propane-4, 4' -oxydiphthalic anhydride copolyimide.

5. The method for preparing a polyimide separator having a thermal shut-off function according to claim 2, wherein the organic solvent in step B may be one or more of N, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, and dichloromethane.

Technical Field

The invention belongs to the technical field of polyimide fiber membranes, and particularly relates to a polyimide battery diaphragm with a thermal pore-closing function and a preparation method thereof.

Background

Lithium batteries have become one of the most potential green energy sources at present due to their advantages of high energy density, long cycle life, and the like. In recent years, lithium batteries have been widely used in the field of daily consumer goods such as mobile phones and automobiles. However, with the continuous popularization of lithium battery applications, the phenomena of battery spontaneous combustion and explosion are also increasing. In order to further develop the lithium battery, the safety of the lithium battery needs to be improved urgently.

The battery diaphragm is an important component for ensuring the safety of the battery as an important component for isolating the positive electrode and the negative electrode and transmitting ions in the battery. The modification of the battery diaphragm is the hot content of the safety research of the lithium battery at present. At present, PE and PP are commonly used as raw materials for commercial diaphragms, and the materials have certain defects in the aspect of thermal stability. There have been a great deal of research on high thermal stability battery separator materials. For example, patent CN201810223944.3 reports a method of mixing an aromatic polymer and ceramic powder to obtain a slurry, coating the slurry on a separator to obtain a heat-resistant battery separator; patent CN201810097336.2 reports a high temperature resistant lithium battery separator using polyimide as material. In addition, researchers also desire that the separator possess the function of achieving closed cells at certain temperatures. The thermal closed-cell membrane has the functions of closing the pores, blocking current and preventing the explosion of the battery while maintaining the dimensional stability at the temperature higher than the rated value. As in patents cn201822113457.x, CN201310085349.5, the function of thermal closed pores of the membrane is achieved by multilayer coatings.

However, a thermal closed-cell composite battery separator prepared by a coating method will inevitably affect the separator porosity, battery thickness and separator uniformity. In view of these disadvantages, the present invention provides a polyimide battery separator having a thermal shut-off function and a method for directly preparing the same by co-axial electrospinning.

Disclosure of Invention

Aiming at the defect that the coating layer realizes the thermal pore-closing function of the diaphragm, the invention provides a polyimide diaphragm with the thermal pore-closing function and a method for directly preparing the polyimide diaphragm by coaxial electrospinning. The outer layer of the coaxial nanofiber is a thermosetting polyimide shell, so that the excellent thermal stability of the diaphragm is ensured; the inner layer is a thermoplastic polyimide core, so that the diaphragm can have the thermal closed hole performance, the thermal closed hole of the diaphragm can be realized without coating, the thickness and the porosity of the diaphragm are not influenced, the operation is simple and convenient, the uniformity and the integrity of a fiber structure can be ensured, and the excellent electrochemical performance of the battery can be ensured while the safety of the battery is remarkably improved.

A polyimide diaphragm with a thermal pore-closing function is characterized in that the diaphragm is a nanofiber porous membrane, and the thickness of the nanofiber porous membrane is 3-30 mu m; the nano-fiber is of a shell-core structure, the shell layer is made of thermosetting polyimide, the thickness of the shell layer is 50-600nm, and the core layer is made of thermoplastic polyimide and the diameter of the core layer is 50-300 nm.

A preparation method of a polyimide diaphragm with a thermal pore-closing function is characterized by comprising the following steps: a, synthesizing a thermosetting polyimide precursor polyamic acid solution;

b: dissolving thermoplastic polyimide powder in an organic solvent to prepare a hot-melt polyimide solution;

c: adding the polyamide acid solution of the thermosetting polyimide precursor prepared in the step A into an outer needle injector of a coaxial electrostatic spinning device, and adding the thermoplastic polyimide solution obtained in the step B into an inner needle injector of the coaxial electrostatic spinning device for electrostatic spinning to obtain a coaxial nanofiber membrane;

d: and D, performing heating thermal imidization treatment on the nano fiber membrane with the shell-core structure prepared in the step C to obtain the polyimide diaphragm with the thermal hole-closing function.

Further, the solid content of the thermosetting polyamic acid solution in the step A is 5-35 wt%.

Further, the thermosetting polyimide in the step A can be one or more of a PMDA-ODA system, a BTDA-ODA system, a BPDA-ODA system and a 6FDA-ODA system.

Further, the solid content of the hot-melt polyimide solution in the step B is 8-50%.

Further, the hot melt polyimide in step B can be one or more of Polyetherimide (PEI), P84 copolyimide, and BAFL-BAPP-ODPA-s-ODPA copolyimide.

Further, the organic solvent described in step A, B may be NMP, DMAc, DMF, DMSO.

Furthermore, the aperture of the coaxial electrostatic spinning inner needle head is 0.3-0.8mm, and the aperture of the outer needle head is 0.5-1.8 mm.

Further, the spinning voltage is 15-50kV, the receiving distance is 16-30cm, and the humidity is 20% -50%.

Further, the thermal imidization condition in the step D is that the final temperature is 250-350 ℃, and the temperature is kept for 15min-4 h.

Compared with the prior art, the method has the following excellent effects:

1. the preparation method has the advantages of simple preparation process, easy satisfaction of conditions, simple and convenient operation and easy repetition.

2. The porous polyimide battery diaphragm with the thermal pore-closing function, which is prepared by the invention, has the advantages of controllable thickness, good uniformity, high porosity, excellent chemical stability, flame retardance and excellent mechanical property.

3. The porous polyimide diaphragm with the thermal pore-closing function, which is prepared by the invention, can generate thermal pore closing when the battery is overheated, so that the battery is prevented from further thermal runaway, and the safety of the battery is greatly improved. .

Drawings

FIG. 1 is an SEM photograph of a sample prepared in example 1;

FIG. 2 is an SEM photograph of a sample prepared in example 2;

FIG. 3 is an SEM photograph of a sample prepared in example 3;

FIG. 4 is an SEM photograph of a sample obtained in example 4

FIG. 5 is an SEM photograph of a sample prepared in example 5;

FIG. 6 is an SEM photograph of a sample prepared in example 1 after heating at 400 ℃ for 1 hour.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Example 1

PEI was dissolved in NMP to make a 20% solids dope and the solution was placed in an inner needle syringe. Preparation of a solid content of 12% of the PMDA/ODA system Polyamic acid was placed in an external syringe. Spinning and cyclizing to obtain the high-temperature-resistant flame-retardant porous polyimide battery diaphragm. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving the ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving the ODA in the DMF, adding the PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, then filling the polyamic acid solution into a 20ml syringe, and connecting an outer needle; (2) weighing 7.71g of PEI, dissolving in 30ml of N-methylpyrrolidone (NMP) solvent under the water bath heating condition of 60 ℃, mechanically stirring for 5h, putting the solution into a 20ml syringe after all the PEI is dissolved, and connecting an inner needle; (3) the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are as follows: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 80.0 m/min; receiving distance: 28 cm; placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; (4) and (3) placing the obtained polyamic acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 30min to obtain the porous polyimide battery diaphragm with the thermal pore-closing function, wherein the fiber appearance is shown in figure 1, the sample is subjected to heat preservation for 1h at the temperature of 400 ℃, and the diaphragm realizes the pore-closing function, and the appearance is shown in figure 6.

Example 2

PVDF was dissolved in NMP to make a spinning solution with 20% solid content, and the solution was placed in an inner needle syringe. Preparation of a solid content of 12% of the PMDA/ODA system Polyamic acid was placed in an external syringe. Spinning and cyclizing to obtain the high-temperature-resistant flame-retardant porous polyimide battery diaphragm. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving the ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving the ODA in the DMF, adding the PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, then filling the polyamic acid solution into a 20ml syringe, and connecting an outer needle; (2) weighing 7.71g of PVDF, dissolving in 30ml of N-methylpyrrolidone (NMP) solvent under the water bath heating condition of 60 ℃, mechanically stirring for 5 hours, putting the solution into a 20ml syringe after all the solution is dissolved, and connecting an inner needle; (3) the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are as follows: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 80.0 m/min; receiving distance: 28 cm; placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; (3) and (3) placing the obtained polyamic acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 30min to obtain the polyimide battery diaphragm with the thermal hole-closing function, wherein the fiber morphology is shown in figure 2.

Example 3

P84 was dissolved in NMP to make a 20% solids spinning solution, which was placed in an inner needle syringe. Preparation of a solid content of 12% of the PMDA/ODA system Polyamic acid was placed in an external syringe. Spinning and cyclizing to obtain the high-temperature-resistant flame-retardant porous polyimide battery diaphragm. (1) Weighing 2.0g of pyromellitic dianhydride (PMDA) and 1.8g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving the ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving the ODA in the DMF, adding the PMDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2 hours, then filling the polyamic acid solution into a 20ml syringe, and connecting an outer needle; (2) weighing 7.71g of P84 copolymerized polyimide, dissolving in 30ml of N-methylpyrrolidone (NMP) solvent under the water bath heating condition of 60 ℃, mechanically stirring for 5 hours, putting the solution into a 20ml syringe after all the solution is dissolved, and connecting an inner needle; (3) the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are as follows: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 80.0 m/min; receiving distance: 28 cm; placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; (3) and (3) placing the obtained polyamic acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 30min to obtain the polyimide battery diaphragm with the thermal hole-closing function, wherein the fiber morphology is shown in figure 3.

Example 4

P84 was dissolved in NMP to make a 20% solids spinning solution, which was placed in an inner needle syringe. Preparation of a 12% solids BTDA/ODA system Polyamic acid was placed in an outer needle syringe. Spinning and cyclizing to obtain the high-temperature-resistant flame-retardant porous polyimide battery diaphragm. (1) Weighing 2.4g of 3,3',4,4' -benzophenonetetracarboxylic dianhydride (BTDA) and 1.5g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding BTDA step by step under the condition of ice-water bath to obtain a polyamic acid solution with viscosity, mechanically stirring for 2h, filling the polyamic acid solution into a 20ml syringe, and connecting an outer needle head; (2) weighing 7.71g of P84 copolymerized polyimide, dissolving in 30ml of N-methylpyrrolidone (NMP) solvent under the water bath heating condition of 60 ℃, mechanically stirring for 5 hours, putting the solution into a 20ml syringe after all the solution is dissolved, and connecting an inner needle; (3) the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are as follows: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 80.0 m/min; receiving distance: 28 cm; placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; (3) and (3) placing the obtained polyamic acid fiber membrane in a heating furnace, gradually heating to 300 ℃ at the heating rate of 2 ℃/min, and keeping for 30min to obtain the polyimide battery diaphragm with the thermal hole-closing function, wherein the fiber morphology is shown in figure 4.

Example 5

P84 was dissolved in NMP to make a 20% solids spinning solution, which was placed in an inner needle syringe. Preparation of an ODPA/ODA System Polyamic acid with a solids content of 12% was placed in an external syringe. Spinning and cyclizing to obtain the high-temperature-resistant flame-retardant porous polyimide battery diaphragm. (1) Weighing 2.3g of 4,4 '-diphenyl ether dianhydride (ODPA) and 1.5g of 4,4' -diaminodiphenyl ether (ODA) in a molar ratio of 1:1, completely dissolving the ODA in 30ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving the ODA in the DMF, adding the ODPA step by step under the condition of ice-water bath to obtain a polyamic acid solution with moderate viscosity, mechanically stirring for 2h, then filling the polyamic acid solution into a 20ml syringe, and connecting an outer needle; (2) weighing 7.71g of P84 copolymerized polyimide, dissolving in 30ml of N-methylpyrrolidone (NMP) solvent under the water bath heating condition of 60 ℃, mechanically stirring for 5 hours, putting the solution into a 20ml syringe after all the solution is dissolved, and connecting an inner needle; (3) the polyamide acid fiber membrane is prepared by applying an electrostatic spinning technology, wherein the parameters of the electrostatic spinning machine are as follows: 17 kV; spinning temperature: room temperature; spinning humidity: 30 percent; diameter of syringe needle: number 12; receiving roller rotating speed: 80.0 m/min; receiving distance: 28 cm; placing the prepared polyamic acid fiber membrane in a super clean bench for 12 h; (3) and (3) placing the obtained polyamic acid fiber membrane in a heating furnace, gradually raising the temperature by 300 ℃ at the temperature raising speed of 2 ℃/min, and keeping the temperature for 30min, so as to obtain the polyimide battery diaphragm with the thermal hole-closing function, wherein the shape of the fiber is shown in figure 5.