A polyimide porous membrane, a method for preparing the same, and an application thereof

Abstract

The present application relates to a kind of polyimide porous membrane and its preparation method and application. Wherein the polyimide porous membrane is the polyimide porous membrane of chemical grafting polyamino compound, polyether compound. The polyimide porous membrane of the present application has low porosity, good thermal stability, good dimensional stability, and the lithium ion battery assembled thereby has higher lithium ion conductivity, higher cycle performance and rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer-based porous membrane materials, in particular to a preparation method of a polyimide porous membrane, which can be applied to lithium ion batteries. BACKGROUND

[0002] In the past two decades, rechargeable lithium ion batteries have led a new energy revolution and become an integral part of our modern life. The rapid development of electronic products requires lithium ion batteries with higher energy density, which poses challenges to the key materials inside the batteries. Among the basic components of lithium ion batteries, the separator serves as a physical barrier between the positive and negative electrodes to prevent internal short circuit, and at the same time provides a tunnel for lithium ion migration with the help of liquid electrolyte during the charge and discharge cycle. However, the further development of lithium ion batteries is restricted by the insufficient thermal performance and poor electrolyte affinity of traditional polyolefin separators.

[0003] Polyimide nanofiber separators are expected to become a candidate material for the next generation of high-performance lithium ion battery separators due to their excellent high-temperature resistance and good electrolyte affinity. However, polyimide separators based on electrospinning still have problems such as high porosity and insufficient ionic conductivity. Reducing the porosity of the material will directly affect the conductivity of lithium ions and thus the rate and cycle performance of the finished battery.

[0004] Polyethylene oxide has been widely used in the research of polymer solid-state batteries due to its ability to conduct lithium ions. However, polyethylene oxide cannot be directly applied to traditional lithium ion batteries due to its poor heat resistance and low mechanical strength.

[0005] Therefore, it is necessary to develop a lithium ion battery separator material with low porosity, good thermal stability and good dimensional stability. SUMMARY

[0006] In view of the above defects of the prior art, the present application provides a polyimide porous membrane with low porosity, good thermal stability and good dimensional stability.

[0007] The technical purpose of the present application is achieved by the following technical solutions:

[0008] The present application provides a polyimide porous membrane, which is a polyimide porous membrane chemically grafted with polyamino compounds and polyether compounds.

[0009] Further, the polyimide porous membrane according to the present application has a thickness of 5-100 μm, a porosity of 40-90%, a shrinkage of less than 1%, a volume resistance of 0.5-10 Ω, and an ionic conductivity of 0.50-3.5 mScm -1Preferably, the polyimide porous membrane has a thickness of 15-30 μm, a porosity of 60%-70%, a shrinkage of less than 1%, a volume resistance of 1.31-3.4 Rb, and an ionic conductivity of 0.50-3.5 mScm -1 .

[0010] Another technical purpose of the present application is to provide a preparation method of the above polyimide porous membrane, comprising the following steps: S1, immersing a polyimide porous base film in a polyamino compound solution, washing, drying, and obtaining a polyamino compound grafted polyimide porous membrane; S2, immersing the polyamino compound grafted polyimide porous membrane in a polyether solution, washing, drying, and obtaining the polyimide porous membrane.

[0011] Further, the polyamino compound solution is obtained by dissolving a polyamino compound in one or more than two solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, water, ethanol, and acetone; the polyamino compound is selected from polyethyleneimine and / or amino-modified silica; preferably, the weight average molecular weight of the polyethyleneimine is 500-5000; preferably, the average particle size of the amino-modified silica is 5-45 nm.

[0012] Further, the preparation method of the polyamino compound solution is as follows: dissolving a polyamino compound in one or more than two solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, and tetrahydrofuran, and stirring after adding a strong base to obtain the polyamino compound solution; the polyamino compound is selected from octaammonium POSS; preferably, the addition amount of the strong base is 6-8 times the molar equivalent of octaammonium POSS; preferably, the strong base is selected from sodium hydroxide or potassium hydroxide.

[0013] Further, the weight ratio of the polyimide porous base film to the polyamino compound is 1:1-1:5; preferably, the mass concentration of the polyamino compound solution is 2-30%; preferably, the immersion temperature of the polyimide porous base film in the polyamino compound solution is 30-120℃, and the immersion time is 2-24 h.

[0014] Further, the polyether solution is obtained by dissolving a polyether in one or more than two solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; preferably, the mass concentration of the polyether solution is 2%-30%.

[0015] Further, the polyether is selected from one or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and bisphenol A diglycidyl ether; preferably, the polyethylene glycol diglycidyl ether has a weight average molecular weight of 500-5000; preferably, the polypropylene glycol diglycidyl ether has a weight average molecular weight of 500-5000.

[0016] Further, the weight ratio of the polyamino compound grafted polyimide porous membrane to the polyether is 1:1-1:5; preferably, the polyamino compound grafted polyimide porous membrane is soaked in the polyether solution at a temperature of 30-120℃ for 2-24h.

[0017] Another technical purpose of the present application is to provide the use of the above-mentioned polyimide porous membrane in a battery, including a lithium ion battery, a lithium-sulfur battery, a vanadium battery, or a fuel cell.

[0018] The present application has the following beneficial effects over the prior art:

[0019] The present application soaks a polyimide porous membrane in a polyamino compound solution to obtain a polyimide porous membrane with a chemically grafted surface, and then soaks the polyimide porous membrane in a polyether solution to obtain a polyimide porous membrane with a grafted polyether structure on the surface. This method obtains a high-performance polyimide porous membrane with low porosity, good thermal stability, and good dimensional stability, and a lithium ion battery assembled therefrom has high lithium ion conductivity, high cycle performance, and high rate performance. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the SEM picture of Example 1 and Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0021] In order to better illustrate the technical purposes, technical solutions, and advantages of the present application, the present application will be further described in conjunction with the drawings and specific examples.

[0022] The design principle of the present application is to soak a nano polyimide in a polyamino compound solution, graft the polyamino compound onto the nano polyimide porous membrane by ring-opening reaction between the amino group and the imide ring, wash away the unreacted polyamino compound, then soak the obtained polyimide porous membrane in a polyether solution containing an epoxy structure, graft the polyether containing ether bond segments onto the polyimide porous membrane by ring-opening reaction between the amino group and the epoxy group, and finally wash away the unreacted polyether to obtain the polyimide porous membrane.

[0023] The polyimide porous base film used in the application is a polyimide nanofiber non-woven fabric; the amino-modified silicon dioxide used in the embodiments of the application is water-soluble amino-modified silicon dioxide, which is purchased from Xi'an Qiyue Biology, and the particle size of the water-soluble amino-modified silicon dioxide is 30 nm; and the octaammonium POSS is purchased from Xi'an Qiyue Biology.

[0024] I. Polyimide porous membrane and preparation method thereof

[0025] Example 1

[0026] 10 g of polyethyleneimine (PEI, Mw = 1000) liquid was dropped into 90 g of N,N-dimethylformamide (DMF) and stirred to prepare a 10 wt% PEI solution. 5 g of polyimide nanofiber non-woven fabric was completely immersed in 100 g of the PEI solution of DMF, reacted at 70°C for 3 h, then rinsed with ethanol for 3 times to remove unreacted PEI molecules, and dried in a 80°C circulating oven for 24 h to obtain a surface-aminated polyimide nanofiber non-woven fabric.

[0027] 10 g of polyethylene glycol diglycidyl ether (PEGDE, Mw = 1000) liquid was dropped into 90 g of DMF and stirred to prepare a 10 wt% polyethylene glycol diglycidyl ether DMF solution. The obtained 5.5 g of polyimide nanofiber non-woven fabric was completely immersed in the polyethylene glycol diglycidyl ether DMF solution, reacted at 70°C for 24 h, and rinsed with ethanol for 3 times to remove unreacted PEGDE molecules. After complete drying in a 80°C vacuum oven overnight, a polyethyleneimine-polyethylene glycol grafted polyimide nanofiber membrane was obtained.

[0028] Example 2

[0029] 5 g of octaammonium POSS was dissolved in 95 g of tetrahydrofuran (THF) and stirred to prepare a 5 wt% POSS solution, and 8 molar equivalents of sodium hydroxide were added dropwise, and stirred at room temperature for 12 h. 5 g of polyimide nanofiber non-woven fabric was completely immersed in the aforementioned POSS solution, reacted at 70°C for 3 h, then rinsed with THF for 3 times to remove unreacted POSS molecules, and completely dried in a 80°C circulating oven to obtain a surface-aminated polyimide nanofiber non-woven fabric containing a POSS bridged structure.

[0030] A 10 g polypropylene glycol diglycidyl ether (Mw = 1000) liquid was dropped into 90 g of DMF and stirred to make a 10 wt% polypropylene glycol diglycidyl ether DMF solution. The resulting 5.5 g polyimide nanofiber nonwoven was completely immersed in the resulting polypropylene glycol diglycidyl ether DMF solution and reacted at 70 °C for 24 h and rinsed with ethanol 3 times to remove unreacted polypropylene glycol diglycidyl ether molecules. After complete drying in a 60 °C vacuum oven overnight, an octaammonium POSS-polypropylene glycol grafted polyimide nanofiber separator was obtained.

[0031] Example 3

[0032] A 15 g polyethyleneimine (PEI, Mw = 1000) liquid was dropped into 85 g of DMF and stirred to make a 15 wt% PEI solution. 5 g of polyimide nanofiber nonwoven was completely immersed in the PEI solution, reacted at 70 °C for 3 h, and then rinsed with ethanol 3 times to remove unreacted PEI molecules, and completely dried in a 80 °C circulating oven to obtain a surface aminated polyimide nanofiber nonwoven.

[0033] A 15 g of bisphenol A diglycidyl ether was dropped into 85 g of DMF and stirred to make a 15 wt% bisphenol A diglycidyl ether DMF solution. The resulting 5.5 g polyimide nanofiber nonwoven was completely immersed in 100 g of DMF solution containing 15 wt% bisphenol A diglycidyl ether, reacted at 70 °C for 24 h, and rinsed with ethanol 3 times to remove unreacted bisphenol A diglycidyl ether molecules. After complete drying in a 60 °C vacuum oven overnight, a polyethyleneimine-bisphenol A grafted polyimide nanofiber separator was obtained.

[0034] Example 4

[0035] A 5 g of octaammonium POSS was dissolved in 95 g of tetrahydrofuran and stirred to make a 5 wt% POSS solution, 8 times molar equivalent of sodium hydroxide was added and stirred at room temperature for 12 h. 5 g of polyimide nanofiber nonwoven was completely immersed in the aforementioned POSS solution, reacted at 70 °C for 3 h, and then rinsed with distilled water 3 times to remove unreacted POSS molecules, and completely dried in a 80 °C circulating oven to obtain a surface aminated polyimide nanofiber nonwoven containing silica bridged structure.

[0036] A solution of 15 g of bisphenol A diglycidyl ether in 85 g of DMF was prepared by stirring to homogeneity. The resulting 5.5 g of polyimide nanofiber nonwoven was completely immersed in the solution of bisphenol A diglycidyl ether in DMF and reacted at 70 °C for 24 h, and rinsed with ethanol three times to remove unreacted bisphenol A diglycidyl ether molecules. After complete drying in a vacuum oven at 60 °C overnight, an octaamino-POSS-bisphenol A grafted polyimide nanofiber separator was obtained.

[0037] Example 5

[0038] A solution of 5 g of aminomodified silica in water was prepared by stirring to homogeneity at room temperature for 12 h. The resulting 5.5 g of polyimide nanofiber nonwoven was completely immersed in the solution of aminomodified silica and reacted at 70 °C for 3 h, and dried completely in a circulating oven at 80 °C to obtain a polyimide nanofiber nonwoven containing a POSS bridged structure surface aminated.

[0039] A solution of 10 g of polypropylene glycol diglycidyl ether in 90 g of DMF was prepared by stirring to homogeneity. The resulting 5.5 g of polyimide nanofiber nonwoven was completely immersed in the solution of polypropylene glycol diglycidyl ether in DMF and reacted at 70 °C for 24 h, and rinsed with ethanol three times to remove unreacted polypropylene glycol diglycidyl ether molecules. After complete drying in a vacuum oven at 60 °C overnight, a silica-polypropylene glycol grafted polyimide nanofiber separator was obtained.

[0040] Comparative Example 1

[0041] Celgard 2320 commercialized separator.

[0042] Comparative Example 2

[0043] Commercialized polyimide separator.

[0044] II. Performance parameter test

[0045] In Examples 1-3 and Comparative Examples 1-2, the performance parameters were tested according to the following methods:

[0046] (1) Porosity

[0047] The porosity of the separator was determined by the n-butanol absorption method and calculated according to the following equation.

[0048] Porosity (%) = (M b - M0) / (p x V) x 100%

[0049] In the equation, M0and M bWd and Wn are the weights of the dry and n-butanol-saturated membranes, respectively, and p is the density of n-butanol (0.8098 g·cm -3 ).

[0050] (2) Volume resistance and lithium ion conductivity

[0051] The volume resistance (R b ) was determined from the intercept with the horizontal axis of the electrochemical impedance spectroscopy (EIS) spectrum of a stainless steel / membrane / stainless steel symmetric cell at a frequency range of 5 x 10 -2 to 5 x 10 5 Hz with an amplitude of 5 mV. The ion conductivity (σ) of the membrane was calculated according to the following equation.

[0052] σ = d / (R x S)

[0053] where d and S represent the thickness and effective area of the membrane, respectively, and R is the volume resistance of the membrane.

[0054] (3) Dimensional stability

[0055] The dimensional stability was taken as the thermal shrinkage rate as a technical index.

[0056] Dimensional stability test: The sample was measured for the sample diameter L1 at room temperature 25℃, then placed in a preheated oven for heat preservation, the oven temperature was 150℃, the heat preservation time was 30 min, the sample was taken out, cooled to room temperature 25℃, the sample diameter L2 was measured again, the change rate of the obtained data L2 / L1 was the thermal shrinkage rate, and the unit was %.

[0057] The porous membranes of Examples 1-3 and Comparative Example 1 were cut into battery separators with a diameter of 19 mm, and the thickness, porosity, volume resistance, thermal stability and ion conductivity of the symmetric cell were tested, and the results are shown in Table 1 below.

[0058] Table 1 Comparison of the properties of the porous membranes prepared in Examples 1-3 and Comparative Example 1-2

[0059]

[0060] According to the data in Table 1 above, the following conclusions can be drawn:

[0061] Comparing Examples 1-3 with Comparative Example 1, i.e., the chemically modified polyimide porous membrane and the traditional Celgard membrane, the thermal shrinkage of the porous membrane is significantly improved, while the volume resistance of the porous membrane is significantly reduced, and the ionic conductivity is significantly improved. By comparing Examples 1-3 with Comparative Example 2, it can be concluded that chemically grafting polymer chains containing ether bonds on polyimide nanofibers can significantly improve the ionic conductivity of the porous membrane and slightly reduce the porosity of the porous membrane, while reducing the volume resistance of the battery. Example 1-3 has a higher porosity than Comparative Example 1 (41), but is slightly lower than Comparative Example 2 (70.1). Although Comparative Example 2 has a slightly higher porosity, the ionic conductivity of the membrane (0.53) is much lower than that of Example 1-3 (2.33, 1.85, 0.90), and the volume resistance value (4.93) is much higher than that of Example 1-3 (1.31, 1.65, 3.4). This further demonstrates that the preparation method of the present invention can significantly improve the lithium ion transmission performance.

[0062] like Figure 1 As shown, by comparing the SEM images of Example 1 and Comparative Example 2, it can be clearly seen that after the porous membrane is grafted with polyethyleneimine and polyether, the pore size and pore size distribution are significantly reduced.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. In addition, the present invention may also be implemented in other ways. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present invention may be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present invention.

Claims

1. A polyimide porous membrane, characterized by, The polyimide porous membrane is a polyimide porous membrane chemically grafted with a polyamino compound and a polyether compound; the polyamino compound is selected from polyethyleneimine and / or amino-modified silica; the polyimide porous membrane has a thickness of 5-100 μm, a porosity of 40-90 %, a shrinkage of less than 1 %, a volume resistance of 0.5-10 Ω, and an ionic conductivity of 0.50-3.5 mScm -1 ; and the polyether is selected from one or two or more of polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, and bisphenol A diglycidyl ether.

2. A method for producing the polyimide porous film according to claim 1, characterized by, The method comprises the following steps: S1: immersing a polyimide porous base film in a polyamino compound solution, washing, drying, and obtaining a polyamino compound grafted polyimide porous film; S2: immersing the polyamino compound grafted polyimide porous film in a polyether solution, washing, drying, and obtaining the polyimide porous film.

3. The method for producing a polyimide porous membrane according to claim 2, characterized by, The polyamino compound solution is obtained by dissolving a polyamino compound in one or more than two solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, water, ethanol, and acetone.

4. The preparation method according to claim 3, characterized in that The weight ratio of the polyimide porous base film to the polyamino compound is 1:1-1:

5.

5. The preparation method according to claim 4, characterized in that: The mass concentration of the polyamino compound solution is 2-30%.

6. The method for producing a polyimide porous membrane according to claim 2, characterized by, The polyether solution is obtained by dissolving a polyether in one or more than two solvents selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

7. The method for producing a polyimide porous membrane according to claim 6, characterized by, The mass concentration of the polyether solution is 2-30%.

8. The method for producing a polyimide porous membrane according to claim 7, characterized by, The weight ratio of the polyamino compound grafted polyimide porous film to the polyether ranges from 1:1 to 1:

5.

9. Use of the polyimide porous membrane according to any one of claims 1 to 8 as a battery separator. The battery comprises a lithium ion battery, a lithium-sulfur battery, a vanadium battery, or a fuel cell.

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