PI nanofiber membrane for lithium battery and preparation method

Abstract

The invention discloses a PI nanofiber membrane for a lithium battery and a preparation method of the PI nanofiber membrane. The preparation method comprises the following steps: selecting proper dianhydride monomers, diamine monomers and polar aprotic solvents; the method comprises the following steps: mixing a diamine monomer with a solvent under an anhydrous condition to form a solution; adding a dianhydride monomer under a low-temperature condition, and slowly heating to carry out a reaction, so as to prepare a polyamide acid solution for later use; the preparation method comprises the following steps: taking a polyamide acid solution, adding the polyamide acid solution into a DMAC (dimethylacetamide) solvent, fully mixing, assembling into an ejector of an electrostatic spinning device, spinning under high voltage, receiving spun yarns through a rotating roller, and collecting for a period of time to obtain the PAA nanofiber non-woven fabric membrane. And the PI nanofiber membrane can be stretched at a higher stretch ratio during subsequent stretching, so that the mechanical property of the obtained PI nanofiber membrane is further improved, the safety characteristic of a lithium battery can be effectively improved, and the rate discharge characteristic of the lithium ion battery and the cycle characteristic of a power product can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery separators, and in particular to a PI nanofiber membrane for lithium batteries and a preparation method thereof. Background Art

[0002] As a high-performance engineering plastic, polyimide (PI) is widely used in aerospace, electrical insulation, atomic energy industry, national defense construction, environmental industry, protection industry, medical and health care and other harsh fields due to its excellent heat resistance, dielectric properties, low temperature resistance, radiation resistance and other characteristics. As a component of lithium-ion batteries, the separator does not participate in the electrochemical reaction, but plays an important role in isolating the positive and negative electrodes and transmitting lithium ions. Currently used commercial polyolefin separators such as PP and PE have the advantages of good mechanical strength and low cost.

[0003] Electrospinning to prepare PI nanofibers usually adopts a two-step method: first, the polyamic acid solution is subjected to electrospinning technology to obtain polyamic acid fibers, and then the PAA is imidized by thermal conversion or chemical conversion, and dehydration and cyclization are performed to generate a PI fiber membrane. However, electrospinning often results in nanofibers with a size of tens to hundreds of nanometers, which often cause short circuits in battery separators due to the large pore structure. Due to the non-oriented stacking, the contact area is small relative to its diameter, so the mechanical properties are insufficient, which poses a hidden danger in the application scenario of power batteries. For this reason, the present application proposes a PI nanofiber membrane for lithium batteries and a preparation method thereof. Summary of the invention

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

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a PI nanofiber membrane for a lithium battery, comprising the following steps: S1. Selecting appropriate dianhydride monomers, diamine monomers and polar aprotic solvents; S2. Under anhydrous conditions, mixing the diamine monomer and the solvent to form a solution; S3, adding dianhydride monomers under low temperature conditions, and slowly raising the temperature to allow the reaction to proceed, thereby obtaining a polyamic acid solution for standby use; S4, taking the polyamic acid solution and adding it to the DMAC solvent to mix thoroughly, and assembling it into the ejector of the electrospinning device, spinning under high voltage, receiving the spinning by rotating the drum, and collecting it for a period of time to obtain the PAA nanofiber nonwoven membrane; S5. Place the prepared PAA nanofiber nonwoven membrane in an oven, and obtain the desired PI nanofiber membrane after heating and thermal imidization.

[0006] Preferably, the dianhydride monomer in step S1 is one of biphenyl dianhydride, ketone group-containing aromatic dianhydride and ester bond-containing aromatic dianhydride.

[0007] Preferably, the diamine monomer in step S1 is one of a benzimidazole diamine monomer and an amide diamine monomer, or a mixture of the two.

[0008] Preferably, the polar aprotic solvent in step S1 is one of dimethylacetamide and N-methylpyrrolidone.

[0009] Preferably, the low temperature condition in step S3 is 0-15°C, and the temperature after heating is 15-50°C.

[0010] Preferably, the injector in step S4 is equipped with a metal needle, and the metal needle is connected to the positive electrode of the high voltage power supply.

[0011] Preferably, the spinning pressure in step S4 is 15-25 kV, and the receiving distance between the ejector and the drum is 15-50 cm.

[0012] Preferably, the heating temperature of the oven in step S5 is 300-360° C., and the insulation time is 30-60 minutes.

[0013] Preferably, the PI nanofiber membrane has an average nanofiber diameter of less than 20 nm, a diameter standard deviation of less than 5 nm, a fiber membrane thickness standard deviation of less than 3 μm, a tensile strength of 79-103 MPa, an elongation at break of 4%-7%, and a thermal decomposition temperature of 523-564°C.

[0014] Compared with the prior art, the beneficial effects of the present invention are: after the polyamic acid is partially chemically imidized, the mechanical strength of the obtained partially imidized polyamic acid film is relatively improved, and it can be stretched at a higher stretching ratio during subsequent stretching, thereby further improving the mechanical properties of the obtained PI nanofiber membrane, which can effectively improve the safety characteristics of lithium batteries, improve the rate discharge characteristics of lithium-ion batteries, and the cycle characteristics of power products. DETAILED DESCRIPTION

[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 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.

[0017] The present invention provides a technical solution: A method for preparing a PI nanofiber membrane for a lithium battery comprises the following steps: S1. Selecting appropriate dianhydride monomers, diamine monomers and polar aprotic solvents; S2. Under anhydrous conditions, mixing the diamine monomer and the solvent to form a solution; S3, adding dianhydride monomers under low temperature conditions, and slowly raising the temperature to allow the reaction to proceed, thereby obtaining a polyamic acid solution for standby use; S4, taking the polyamic acid solution and adding it to the DMAC solvent to mix thoroughly, and assembling it into the ejector of the electrospinning device, spinning under high voltage, receiving the spinning by rotating the drum, and collecting it for a period of time to obtain the PAA nanofiber nonwoven membrane; S5. Place the prepared PAA nanofiber nonwoven membrane in an oven, and obtain the desired PI nanofiber membrane after heating and thermal imidization.

[0018] The dianhydride monomer in step S1 is one of biphenyl dianhydride, ketone group-containing aromatic dianhydride and ester bond-containing aromatic dianhydride.

[0019] The diamine monomer in step S1 is one of a benzimidazole diamine monomer and an amide diamine monomer or a mixture of the two.

[0020] Wherein, the polar aprotic solvent in step S1 is one of dimethylacetamide and N-methylpyrrolidone.

[0021] The low temperature condition in step S3 is 0-15°C, and the temperature after heating is 15-50°C.

[0022] Wherein, the injector in step S4 is equipped with a metal needle, and the metal needle is connected to the positive electrode of the high voltage power supply.

[0023] The spinning pressure in step S4 is 15-25 kV, and the receiving distance between the ejector and the drum is 15-50 cm.

[0024] Wherein, the heating temperature of the oven in step S5 is 300-360° C., and the insulation time is 30-60 minutes.

[0025] Among them, the average diameter of nanofibers of PI nanofiber membrane is less than 20nm, the standard deviation of diameter is less than 5nm, the standard deviation of fiber membrane thickness is less than 3μm, the tensile strength is 79-103Mpa, the elongation at break is 4%-7%, and the thermal decomposition temperature is 523-564℃.

[0026] Embodiment 1:

[0027] Select appropriate biphenyl dianhydride, benzimidazole diamine monomer and dimethylacetamide; under anhydrous conditions, mix the benzimidazole diamine monomer and dimethylacetamide to form a solution; add biphenyl dianhydride under a low temperature condition of 0°C, and slowly raise the temperature to 15°C to allow the reaction to proceed, thereby obtaining a polyamic acid solution for use; take the polyamic acid solution and add it to the DMAC solvent to fully mix, and assemble it into the ejector of the electrospinning device, spin at a high voltage of 15kV, control the receiving distance between the ejector and the roller to be 15cm, and rotate The spinning is received by a moving drum and collected for a period of time to obtain a PAA nanofiber non-woven fabric membrane; the prepared PAA nanofiber non-woven fabric membrane is placed in an oven and heated to 300°C and kept warm for 30 minutes, and the desired PI nanofiber membrane is obtained after heating and thermal imidization. The obtained PI nanofiber membrane has excellent mechanical properties, with an average nanofiber diameter of 18nm, a diameter standard deviation of less than 3nm, a fiber membrane thickness standard deviation of less than 3μm, a tensile strength of 79Mpa, an elongation at break of 5%, and a thermal decomposition temperature of 523°C.

[0028] Embodiment 2:

[0029] Select appropriate keto-group-containing aromatic dianhydride, amide diamine monomer and dimethylacetamide; under anhydrous conditions, mix the amide diamine monomer and dimethylacetamide to form a solution; add keto-group-containing aromatic dianhydride under low temperature conditions of 8°C, and slowly raise the temperature to 35°C to allow the reaction to proceed, thereby obtaining a polyamic acid solution for use; take the polyamic acid solution and add it to the DMAC solvent to fully mix, and assemble it into the ejector of the electrospinning device, spin at a high voltage of 17kV, control the receiving distance between the ejector and the roller to be 25cm, and pass The spinning is received by a rotating drum and collected for a period of time to obtain a PAA nanofiber non-woven membrane; the prepared PAA nanofiber non-woven membrane is placed in an oven and heated to 320°C and kept warm for 45 minutes, and the desired PI nanofiber membrane is obtained after heating and thermal imidization. The obtained PI nanofiber membrane has excellent mechanical properties, with an average nanofiber diameter of 16nm, a diameter standard deviation of less than 3nm, a fiber membrane thickness standard deviation of less than 3μm, a tensile strength of 93Mpa, an elongation at break of 5%, and a thermal decomposition temperature of 547°C.

[0030] Embodiment 3:

[0031] Select appropriate ester-bonded aromatic dianhydride, benzimidazole diamine monomer and amide diamine monomer mixture and N-methylpyrrolidone; under anhydrous conditions, mix the benzimidazole diamine monomer and amide diamine monomer mixture with N-methylpyrrolidone to form a solution; add ester-bonded aromatic dianhydride under low temperature conditions of 15°C, and slowly raise the temperature to 50°C to allow the reaction to proceed, thereby obtaining a polyamic acid solution for use; take the polyamic acid solution and add it to the DMAC solvent to fully mix, and assemble it into the ejector of the electrospinning device, spin at a high voltage of 20kV, and control the ejector and The receiving distance of the drum is 50cm. The spinning is received by rotating the drum and collected for a period of time to obtain a PAA nanofiber non-woven fabric membrane; the prepared PAA nanofiber non-woven fabric membrane is placed in an oven and heated to 360°C and kept warm for 60 minutes. After heating and thermal imidization, the desired PI nanofiber membrane is obtained. The obtained PI nanofiber membrane has excellent mechanical properties, with an average nanofiber diameter of 12nm, a diameter standard deviation of less than 2nm, a fiber membrane thickness standard deviation of less than 2μm, a tensile strength of 101Mpa, an elongation at break of 7%, and a thermal decomposition temperature of 556°C.

[0032] 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 method for preparing a PI nanofiber membrane for a lithium battery, characterized in that: The following steps are involved: S1. Selecting appropriate dianhydride monomers, diamine monomers and polar aprotic solvents; S2. Under anhydrous conditions, mixing the diamine monomer and the solvent to form a solution; S3, adding dianhydride monomers under low temperature conditions, and slowly raising the temperature to allow the reaction to proceed, thereby obtaining a polyamic acid solution for standby use; S4, taking the polyamic acid solution and adding it to the DMAC solvent to mix thoroughly, and assembling it into the ejector of the electrospinning device, spinning under high voltage, receiving the spinning by rotating the drum, and collecting it for a period of time to obtain the PAA nanofiber nonwoven membrane; S5. Place the prepared PAA nanofiber nonwoven membrane in an oven, and obtain the desired PI nanofiber membrane after heating and thermal imidization.

2. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The dianhydride monomer in step S1 is one of biphenyl dianhydride, ketone group-containing aromatic dianhydride and ester bond-containing aromatic dianhydride.

3. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The diamine monomer in step S1 is one of a benzimidazole diamine monomer and an amide diamine monomer or a mixture of the two.

4. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The polar aprotic solvent in step S1 is one of dimethylacetamide and N-methylpyrrolidone.

5. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The low temperature condition in step S3 is 0-15°C, and the temperature after heating is 15-50°C.

6. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The injector in step S4 is equipped with a metal needle, and the metal needle is connected to the positive electrode of the high voltage power supply.

7. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: The spinning pressure in step S4 is 15-25 kV, and the receiving distance between the ejector and the drum is 15-50 cm.

8. The method for preparing a PI nanofiber membrane for a lithium battery according to claim 1, characterized in that: In step S5, the heating temperature of the oven is 300-360° C., and the heat preservation time is 30-60 minutes.

9. A PI nanofiber membrane for lithium batteries, characterized in that: The average diameter of the nanofibers of the PI nanofiber membrane is less than 20 nm, the standard deviation of the diameter is less than 5 nm, the standard deviation of the fiber membrane thickness is less than 3 μm, the tensile strength is 79-103 MPa, the elongation at break is 4%-7%, and the thermal decomposition temperature is 523-564°C.