A zwitterionic modified polyimide porous membrane, its preparation method and application

Abstract

The application relates to a zwitterion-modified polyimide porous membrane and a preparation method and application thereof. The preparation method of the zwitterion-modified polyimide porous membrane is characterized by introducing zwitterion groups through chemical grafting, thereby preparing the zwitterion-modified polyimide porous membrane, realizing the improvement of the ion conductivity and lithium ion transference number of the diaphragm, and maintaining the excellent mechanical properties of the polyimide.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery separator technology, and in particular to a zwitterionic modified polyimide porous membrane, its preparation method, and its application. Background Technology

[0002] In the basic components of a lithium-ion battery, the separator acts as a physical barrier between the positive and negative electrodes to prevent internal short circuits, while also providing a tunnel for lithium-ion migration during charge-discharge cycles with the help of the liquid electrolyte. However, traditional polyolefin separators have limited the further development of lithium-ion batteries due to insufficient thermal performance and poor electrolyte affinity.

[0003] Polyimide nanofiber separators are promising candidates for next-generation high-performance lithium-ion battery separators due to their excellent high-temperature resistance and good electrolyte affinity. However, polyimide separators based on electrospinning and non-solvent phase transfer still have problems such as insufficient ionic conductivity and low lithium-ion transference number. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a method for preparing a zwitterionic modified polyimide porous membrane. By introducing zwitterionic groups through chemical grafting, a zwitterionic modified polyimide porous membrane is prepared, which has good thermal stability and good dimensional stability. When the prepared zwitterionic modified polyimide porous membrane is applied to lithium-ion battery separators, it can improve the ionic conductivity and lithium-ion transference number of the separator while maintaining the excellent mechanical properties of polyimide.

[0005] The present invention discloses a method for preparing a zwitterionic modified polyimide porous membrane, comprising the following steps:

[0006] S1: Immerse the polyimide-based membrane in a solution of a polyamine compound, then wash and dry to obtain a polyamine compound-grafted polyimide porous membrane;

[0007] S2: The polyamine-grafted polyimide porous membrane was immersed in the grafted compound solution, then washed and dried to prepare the zwitterionic modified polyimide porous membrane.

[0008] Wherein, the polyamino compound is polyethyleneimine; the grafting compound is sulfonyl lactone or acid anhydride;

[0009] In step S2, the immersion temperature is 60-90℃ and the immersion time is 12-24h.

[0010] Preferably, the weight-average molecular weight of the polyethyleneimine is 500-5000.

[0011] The polyimide-based membrane comprises a polyimide nanofiber pad prepared by electrospinning or a polyimide porous membrane prepared by solvent-free phase transfer. The polyimide-based membrane is immersed in a polyethyleneimine solution of a certain concentration. A polyamine compound is grafted onto the polyimide-based membrane using a ring-opening reaction between the amino and imide rings, resulting in a polyamine-grafted polyimide porous membrane. This polyamine-grafted polyimide porous membrane is then immersed in a sulfonyl lactone or anhydride solution of a certain concentration. A quaternization reaction occurs between the amino and sulfonyl lactone or anhydride groups, causing the sulfonyl lactone or anhydride to open its ring and graft onto the surface of the porous channels of the polyimide porous membrane. This achieves the combination of maintaining the good mechanical strength and chemical stability of polyimide with high zwitterionic conductivity and high ion transport number.

[0012] Further, the concentration of the sulfonyl lactone solution or the acid anhydride solution is 2-30 wt%. The method for preparing the sulfonyl lactone solution or acid anhydride solution is as follows: dissolving the sulfonyl lactone or acid anhydride in one or more solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetone in a certain proportion.

[0013] Specifically, the sulfonyl lactones include one or more of propanesulfonyl lactone, butanesulfonyl lactone, pentasulfonyl lactone, and hexanesulfonyl lactone.

[0014] Specifically, the acid anhydride is one or more of maleic anhydride, succinic anhydride, glutaric anhydride, hexahydrophthalic anhydride, and phthalic anhydride.

[0015] Furthermore, the mass ratio of the polyamine-grafted polyimide porous membrane to the grafted compound is in the range of 1:(0.4-6).

[0016] Another technical objective of this invention is to provide the application of the above-mentioned zwitterionic modified polyimide porous membrane in battery separators, wherein the battery includes lithium-ion batteries, lithium-sulfur batteries, vanadium batteries, or fuel cells.

[0017] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0018] Figure 1 This is a schematic diagram illustrating the reaction principle of maleic anhydride as a grafting compound.

[0019] Figure 2 This is a schematic diagram illustrating the reaction principle of glutaric anhydride as a grafting compound.

[0020] Figure 3 This is a schematic diagram illustrating the reaction mechanism of propanesulfonyl lactone as a grafting compound. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1

[0023] In this embodiment, polyimide nanofiber nonwoven fabric is used as the polyimide-based film.

[0024] 10g of polyethyleneimine (PEI, Mw=1000) liquid was added dropwise to 90g of N,N-dimethylformamide (DMF) and stirred until a 10wt% PEI solution was obtained. Polyimide nanofiber nonwoven fabric was thoroughly immersed in the DMF-PEI solution and treated at 70℃ for 3 hours. It was then rinsed three times with ethanol to remove unreacted PEI molecules and completely dried in a circulating oven to obtain a surface-aminated polyamine compound polyimide nanofiber nonwoven fabric.

[0025] Example 2

[0026] Weigh 10g of maleic anhydride and add it to 90g of DMF. Stir well to obtain a 10wt% maleic anhydride solution.

[0027] Five g of the polyamine nanofiber nonwoven fabric prepared in Example 1 was immersed in a solution containing maleic anhydride and soaked at 70°C for 24 hours. It was then rinsed three times with ethanol to remove unreacted maleic anhydride molecules. Next, it was completely dried in a vacuum oven at 60°C for 12 hours to obtain a polyimide nanofiber membrane (i.e., a zwitterionic modified polyimide porous membrane). For details of the reaction principle, please refer to [link to relevant documentation]. Figure 1 .

[0028] Example 3

[0029] Weigh 10g of glutaric anhydride and add it to 90g of DMF. Stir well to obtain a 10wt% glutaric anhydride solution.

[0030] Five g of the polyamine nanofiber nonwoven fabric prepared in Example 1 was immersed in a solution containing glutaric anhydride and soaked at 70°C for 24 hours. It was then rinsed three times with ethanol to remove unreacted glutaric anhydride molecules. Next, it was completely dried in a vacuum oven at 60°C for 12 hours to obtain a polyimide nanofiber membrane (i.e., a zwitterionic modified polyimide porous membrane). For details of the reaction principle, please refer to [link to relevant documentation]. Figure 2 .

[0031] Example 4

[0032] Weigh 30g of propanesulfonyl lactone and add it to 70g of DMF. Stir well to obtain a 30wt% propanesulfonyl lactone solution.

[0033] Five g of the polyamine nanofiber nonwoven fabric prepared in Example 1 was immersed in a solution containing propanesulfonyl lactone and soaked at 60°C for 24 h. It was then rinsed three times with ethanol to remove unreacted propanesulfonyl lactone molecules. Next, it was completely dried in a vacuum oven at 60°C for 12 h to obtain a polyimide nanofiber membrane (i.e., a zwitterionic modified polyimide porous membrane). For details of the reaction principle, please refer to [link to relevant documentation]. Figure 3 .

[0034] Example 5

[0035] Weigh 2g of propanesulfonyl lactone and add it to 98g of DMF. Stir well to obtain a 2wt% propanesulfonyl lactone solution.

[0036] Five g of the polyamine nanofiber nonwoven fabric prepared in Example 1 was immersed in a solution containing propanesulfonyl lactone and soaked at 90°C for 12 hours. It was then rinsed three times with ethanol to remove unreacted propanesulfonyl lactone molecules. Next, it was completely dried in a vacuum oven at 60°C for 12 hours to obtain a polyimide nanofiber membrane (i.e., a zwitterionic modified polyimide porous membrane). For details of the reaction principle, please refer to [link to relevant documentation]. Figure 3 .

[0037] Comparative Example 1

[0038] Celgard 2325 commercially available diaphragm.

[0039] Comparative Example 2

[0040] Commercial polyimide nanofiber nonwoven fabric.

[0041] Performance testing

[0042] The following performance tests were performed on the samples from Examples 1-5 and Comparative Examples 1-2:

[0043] (1) Volume resistivity and lithium-ion conductivity

[0044] Volume resistivity (R) b ) Made of stainless steel / separator / stainless steel symmetrical cells in 5×10 -2 Up to 5×10 5 The ionic conductivity (σ) of the membrane was determined from the intercept of the electrochemical impedance spectroscopy (EIS) spectrum with an amplitude of 5 mV within the Hz frequency range.

[0045] σ=d / (R×S)

[0046] Where d and S represent the thickness and effective area of ​​the diaphragm, respectively.

[0047] (2) Dimensional stability

[0048] Dimensional stability is measured by the rate of thermal shrinkage.

[0049] Dimensional stability test: Take the sample at room temperature (25℃) and measure the sample diameter L1. Then put it into a preheated oven and keep it at 150℃ for 30 minutes. Take out the sample, cool it to room temperature (25℃), and measure the sample diameter L2 again. The change rate of the obtained data L2 / L1 is the heat shrinkage rate, and its unit is %.

[0050] (3) Lithium-ion transport number

[0051] The lithium-ion transport number was evaluated using electrochemical impedance spectroscopy combined with steady-state current technology. The lithium-ion transport number (T+) was measured at an amplitude of 5 mV in the frequency range of 50 mHz to 100 kHz before and after polarization using an AC impedance method assembled with a Li / separator / Li symmetric cell. The lithium-ion transport number (T+) can be calculated using the following equation:

[0052] T + =I s (ΔV-I0R0) / I0(ΔV-I s R s )

[0053] Where R0 and R s These are the initial interface resistance and the steady-state interface resistance, respectively. I0 and I... s These are the initial current and the steady-state current, respectively. ΔV (10mV) is the potential applied to the battery.

[0054] The sample performance test data of Examples 1-5 and Comparative Examples 1-2 are detailed in Table 1.

[0055] Table 1. Sample performance test data for Examples 1-5 and Comparative Examples 1-2

[0056]

[0057]

[0058] Compared with Comparative Examples 2-5 and Comparative Example 1, the zwitterionic modified polyimide porous membrane provided in this application significantly improves the thermal shrinkage rate of the porous membrane compared with the commercially available Celgard 2325 membrane. At the same time, the volume resistivity of the porous membrane is significantly reduced and the ionic conductivity is significantly improved.

[0059] Comparing Comparative Example 2, Example 1, and Examples 2-5, it can be seen that grafting polyamine compounds onto polyimide-based films can reduce the volume resistivity of porous films and increase ionic conductivity and lithium-ion transference number, but the effect is not significant. After further grafting polyamine compounds onto polyimide porous films using sulfonyl lactones or acid anhydrides, the volume resistivity of the porous film significantly decreases, the ionic conductivity is significantly improved, and the thermal shrinkage rate is maintained, resulting in good dimensional stability.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows: by introducing zwitterionic groups through chemical grafting, a zwitterionic modified polyimide porous membrane is prepared, which can improve the ionic conductivity and lithium ion transference number of the membrane while maintaining the excellent mechanical properties of polyimide.

[0061] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A method for producing a zwitterion-modified polyimide porous membrane, characterized by, The method comprises the following steps: S1: immersing a polyimide-based membrane in a polyamino compound solution, then washing, drying, and obtaining a polyamino compound grafted polyimide porous membrane; S2: immersing the polyamino compound grafted polyimide porous membrane in a grafting compound solution, then washing, drying, and preparing a zwitterion-modified polyimide porous membrane; The concentration of the grafting compound solution is 2-30 wt%, the polyamino compound is polyethyleneimine, the grafting compound is a sultone or an anhydride, the sultone includes one or two or more of propylsultone, butylsultone, pentylsultone, and hexylsultone, and the anhydride is one or two or more of maleic anhydride, succinic anhydride, glutaric anhydride, hexahydrophthalic anhydride, and phthalic anhydride.

2. The method of claim 1, wherein the method is characterized by: The polyimide-based membrane is a polyimide nanofiber mat prepared by electrospinning or a polyimide porous base membrane prepared by non-solvent phase transfer.

3. The method for preparing a zwitterionic modified polyimide porous membrane according to claim 1, characterized in that, The preparation method of the grafting compound solution is to dissolve the grafting compound in one or two or more solvents of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetone.

4. The method of claim 1, wherein the method further comprises: In step S2, the immersion temperature is 60-90℃, and the immersion time is 12-24 h.

5. The method for preparing a zwitterionic modified polyimide porous membrane according to claim 1, characterized in that: The mass ratio of the polyamino compound grafted polyimide porous membrane to the grafting compound is 1:(0.4-6).

6. A zwitterion-modified polyimide porous membrane characterized by: The zwitterion-modified polyimide porous membrane is a polyamino compound polyimide porous membrane grafted with a sultone or an anhydride, which is prepared by the preparation method of any one of claims 1-5.

7. Use of the zwitterion-modified polyimide porous membrane according to claim 6 in a battery separator, characterized by: The battery includes a lithium ion battery, a lithium-sulfur battery, a vanadium battery, or a fuel cell.

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