A recycled polyimide separator and a method for preparing the same

Abstract

This invention belongs to the field of polymer materials technology, specifically relating to a recyclable polyimide separator and its preparation method. Partial ring-opening of the polyimide film is achieved through chemical catalysis, followed by dissolution to prepare a polyamic acid solution. This solution is then spun and imidized to obtain a polyimide nanofiber separator suitable for lithium-ion batteries. This reduces the cost of battery separator preparation while achieving high-value-added conversion and utilization of polyimide waste. The polyimide separator obtained by this invention through recycling and respinning has a similar structure and appearance to polyimide separators prepared by the traditional two-step method, exhibiting excellent mechanical properties, thermal stability, and electrochemical performance. Furthermore, the assembled battery performs better than traditional commercial polyolefin separators, meeting the performance requirements of next-generation lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a recyclable polyimide membrane and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their high energy density and long cycle life, are widely used in consumer electronics, new energy vehicles, and energy storage, making them one of the most promising battery technologies. As a core component of lithium-ion batteries, the separator faces increasingly stringent requirements regarding material performance and cost. Currently, traditional commercial separators are mainly made of polyolefin materials, which have low melting points and poor thermal stability. Furthermore, the non-polar nature of polyolefins results in poor electrolyte wettability and low ionic conductivity. Researchers are dedicated to finding next-generation separators with excellent thermal stability. Among these, polyimide separators almost meet all the requirements, effectively addressing key challenges of lithium-ion batteries such as poor thermal stability, low ionic conductivity, and lithium dendrite growth, thus contributing to extended battery life and efficiency.

[0003] However, most existing polyimide lithium-ion battery separators are made from polyimide materials prepared using traditional methods, and the high preparation and processing costs limit their widespread use. The recycling of polyimide materials holds promise for solving these problems. Traditional chemical recycling methods, such as those disclosed in publications CN109503614A, CN111073035A, and CN113354527A, involve the complete degradation of polyimide to recover the monomers. This process suffers from long processing cycles, complex purification processes, and difficult post-processing, making it difficult to directly apply to battery separator preparation. Therefore, developing a method that can prepare high-performance lithium-ion battery separators while effectively treating waste polyimide films is of significant value. Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a recyclable polyimide separator and its preparation method. Partial ring-opening of the polyimide film is achieved through chemical catalysis, followed by solvent dissolution to obtain a processable polyamic acid solution. Further spinning and imidization yield a polyimide separator suitable for lithium-ion batteries. This method is simple to operate, does not require degradation to the monomer level, and effectively addresses the high cost of polyimide separators while efficiently handling waste polyimide films.

[0005] First aspect:

[0006] A method for preparing a recyclable polyimide separator includes the following steps: Waste polyimide film is placed in an inorganic alkaline solution and soaked at 25-100℃ for 1-80 hours to obtain pretreated polyimide film; The pretreated polyimide film was washed with water until no alkaline residue remained on the surface, and then washed in an acid solution to obtain a deep-treated polyimide film. The deep-treated polyimide film was washed with water until no acid residue remained on the surface, dried, and then dissolved in a first organic solvent to obtain a polyamic acid solution. The polyamic acid solution was spun and dried to obtain a polyamic acid nanofiber membrane. The polyamic acid nanofiber membrane is treated at 100-250°C for 10-300 min, then treated in a second solvent for 10-200 s, the second solvent is removed, and then imidization is performed to obtain the recycled polyimide membrane. The first organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, and tetrahydrofuran; The second solvent includes at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, tetrahydrofuran, ethanol, water, and methanol.

[0007] This invention first places waste polyimide films in an inorganic alkaline solution to partially break the imide rings in the waste films, forming a porous pretreated structure. Then, the alkaline residue on the surface of the pretreated polyimide films is washed away with water, followed by washing away alkali metal ions and imide ring breakage products with an acid solution. Next, the acid residue on the surface of the deep-treated polyimide films is washed away with water until neutral, dried, and then dissolved in an organic solvent to prepare a polyamic acid solution for spinning. Finally, the spun polyamic acid nanofiber membrane is treated at a low temperature to partially imidize it, preventing dissolution in the solvent during subsequent solvent treatment. Solvent treatment is used to partially dissolve the nanofibers in the polyamic acid nanofiber membrane, forming fiber crosslinking points, increasing the crosslinking density, and thus improving mechanical strength. If the treatment time is too long, the nanofiber membrane may completely dissolve. After solvent treatment, high-temperature imidization is performed to prepare a polyimide membrane.

[0008] The recycled polyimide membrane prepared by this invention has similar appearance, structure, mechanical properties and electrochemical properties to the polyimide membrane prepared by the traditional two-step method, and is significantly superior to the traditional commercial membrane, showing excellent application prospects.

[0009] As a preferred embodiment, the waste polyimide film is placed in the inorganic alkaline solution, and the resulting pretreated polyimide film can be completely dissolved in the first organic solvent, which is the reaction endpoint.

[0010] As a preferred embodiment, the viscosity of the polyamic acid solution at 30°C is 0.5-2.0 Pa·s. If the viscosity is too low, subsequent spinning cannot be carried out; if the viscosity is too high, it will affect the microstructure of the nanofiber membrane prepared by spinning, or even make spinning unstable.

[0011] As a preferred embodiment, the concentration of the inorganic alkaline solution is 0.1-10 mol / L; the inorganic alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, ammonia, hydrazine hydrate, sodium phosphate, and potassium phosphate solution. Excessive concentration will cause the waste polyimide film to dissolve rapidly and completely degrade into monomers, affecting subsequent processing.

[0012] As a preferred embodiment, the concentration of the acid solution is 0.1-10 mol / L; the acid solution includes at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, and perchloric acid.

[0013] As a preferred embodiment, the imidization temperature is 300-400℃, and the reaction time is 10-300 min. If the reaction temperature is too low, thermal amidation will fail, thus preventing the formation of polyimide; if the reaction temperature is too high, the polymer will decompose.

[0014] As a preferred embodiment, the spinning process includes at least one of electrospinning and centrifugal spinning.

[0015] As a preferred embodiment, the method further includes the following steps: removing visible impurities from the surface of the waste polyimide film, then ultrasonically cleaning it in an alcohol solution, followed by rinsing with deionized water, drying it, and then placing it in the inorganic alkaline solution; the alcohol solution includes at least one of an ethanol solution and a methanol solution.

[0016] First, remove visible impurities from the surface, and then use an alcohol solution for ultrasonic cleaning to remove oily impurities, thereby reducing side reactions and the amount of subsequent acid and alkali solutions used, thus lowering costs.

[0017] The second aspect: A recycled polyimide membrane prepared by the method described in the first aspect has a tensile strength of 17-20 MPa, a volume resistivity of 2.96-3.27 ohms, and an ionic conductivity of 0.67-0.71 mS·cm. -1 The lithium-ion transference number is 0.43-0.45.

[0018] Third aspect: A lithium-ion battery comprising a recycled polyimide separator prepared by the preparation method described in the first aspect.

[0019] Unlike existing chemical recycling technologies, the method of this invention does not require the degradation of polyimide materials into small molecule compounds. Instead, it achieves a partial ring-opening process of the polyimide film through chemical catalysis, obtaining a processable polyimide precursor—a polyamic acid solution. This solution is then spun into a polyamic acid nanofiber membrane, which is subsequently subjected to high-temperature imidization to obtain a polyimide separator. This separator has a structure similar to that of polyimide separators prepared by the traditional two-step method, exhibits similar mechanical, thermal, and electrochemical properties, and produces batteries with comparable performance. Furthermore, it outperforms traditional commercial polyolefin separators, meeting the performance requirements of next-generation lithium-ion batteries. Attached Figure Description

[0020] Figure 1 SEM images of the polyimide membranes prepared in Examples 1-5 and Comparative Example 2.

[0021] Figure 2 ATR-FTIR images of the polyimide membranes prepared in Examples 1-5 and Comparative Example 2. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0023] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] A method for preparing a recyclable polyimide separator includes the following steps: S1, remove visible impurities from the waste polyimide film by immersing it in an alcohol solution for ultrasonic cleaning to remove oil and soluble impurities adhering to the film surface, followed by rinsing with deionized water and drying.

[0028] S2, the washed waste polyimide film is placed in an inorganic alkaline solution and soaked at 25-100℃ for 1-80 hours to break the imide rings in the film, thus obtaining a pretreated polyimide film that can be completely dissolved in the first organic solvent.

[0029] S3. The pretreated polyimide film is washed with water until there is no alkali residue on the surface, and then washed in an acid solution to remove residual alkali metal ions and imide ring cleavage products on the film surface, thus obtaining a deep-treated polyimide film.

[0030] S4. The deep-treated polyimide film is washed with water until there is no acid residue on the surface and the pH is close to neutral. After drying, it is dissolved with the first organic solvent to obtain a polyamic acid solution with a viscosity of 0.5-2.0 Pa·s and a solid content of not less than 35wt%.

[0031] S5. The prepared polyamic acid solution is electrospun or centrifuged and dried to obtain a polyamic acid nanofiber membrane.

[0032] S6. The polyamic acid nanofiber membrane is treated at 100-250℃ for 10-300 min, then immersed in a second solvent for 10-200 s, the second solvent is removed, and imidization is carried out at 300-400℃ for 10-300 min to obtain a recycled polyimide membrane.

[0033] Alcohol solutions include at least one of ethanol solutions and methanol solutions.

[0034] The concentration of the inorganic alkaline solution is 0.1-10 mol / L; the inorganic alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, ammonia, hydrazine hydrate, sodium phosphate, and potassium phosphate solution.

[0035] The concentration of the acid solution is 0.1-10 mol / L; the acid solution includes at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, and perchloric acid.

[0036] The first organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, and tetrahydrofuran.

[0037] The second solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, tetrahydrofuran, ethanol, water, and methanol.

[0038] The prepared recycled polyimide membrane has a tensile strength of 17-20 MPa, a volume resistivity of 2.96-3.27 ohms, and an ionic conductivity of 0.67-0.71 mS·cm. -1 With a lithium-ion transference number of 0.43-0.45, it is suitable for lithium-ion battery separators.

[0039] In the embodiments and comparative examples of this invention, the performance parameters were tested according to the following method: (1) The microscopic surface morphology of the sample was observed using a scanning electron microscope (SEM). The sample was dried for 12 h, sputtered with gold, and then placed in the SEM chamber for observation.

[0040] (2) The sample was characterized by total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The sample was prepared into small circular discs with a diameter of 10 mm, then dried in a vacuum oven at 80 °C to remove moisture, and the diaphragm was then tested. The number of scans was 16, and the scanning range was 500-4000 cm⁻¹. -1 .

[0041] (3) The mechanical properties of the samples were characterized using a dynamic mechanical analyzer (DMA). The samples were cut into strips with dimensions of 3×15 mm and subjected to a dynamic mechanical analyzer at 30 °C at a flow rate of 3 mm·min. -1 Tensile tests were conducted at a certain speed.

[0042] (4) Volume resistivity and lithium-ion conductivity Volume resistivity (Rb) of stainless steel / separator / stainless steel symmetrical cell at 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.

[0043] σ=d / (R×S) Where d and S represent the thickness and effective area of ​​the diaphragm, respectively.

[0044] (5) 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 by AC impedance spectroscopy with an amplitude of 5 mV in the frequency range of 50 mHz to 100 kHz before and after polarization of the Li / membrane / Li symmetric cell assembly. + The following equation can be used to calculate: t + =I s (ΔV-I0R0) / I0(ΔV-I s R s ) 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, and ΔV (10mV) is the potential applied to the battery.

[0045] Example 1 A method for preparing a recyclable polyimide separator includes the following steps: First, visible impurities in the waste polyimide film were removed. The film was then ultrasonically cleaned in an ethanol solution for 30 minutes, rinsed with deionized water, and dried. The pretreated film was then immersed in a 1 mol / L sodium hydroxide solution at 25°C for 80 hours. Afterward, the film was rinsed with deionized water and washed in a 1 mol / L hydrochloric acid solution. It was then rinsed again with deionized water until the pH was close to neutral. After drying, it was dissolved in N,N-dimethylformamide to obtain a polyamic acid solution with a viscosity of 1.2 Pa·s and a solid content of 35 wt%. This solution was used to prepare a polyamic acid nanofiber membrane via electrospinning. The membrane was pretreated at 100°C for 300 minutes, then immersed in ethanol for 200 seconds, and finally imidized at 300°C for 120 minutes to obtain a recycled polyimide membrane.

[0046] Example 2 A method for preparing a recyclable polyimide separator includes the following steps: First, visible impurities in the waste polyimide film were removed by ultrasonic cleaning in methanol solution for 20 min, followed by rinsing with deionized water and drying. The pretreated film was then immersed in a 10 mol / L potassium hydroxide solution at 80 °C for 2 h. Afterward, the film was rinsed with deionized water and washed in a 10 mol / L sulfuric acid solution. It was then rinsed again with deionized water until the pH was near neutral, dried, and dissolved in N,N-dimethylacetamide to obtain a polyamic acid solution with a viscosity of 1.1 Pa·s and a solid content of 40 wt%. This solution was then used to prepare a polyamic acid nanofiber membrane via centrifugal spinning. The membrane was pretreated at 250 °C for 10 min, then immersed in methanol for 100 s, and finally imidized at 400 °C for 30 min to obtain a recycled polyimide membrane.

[0047] Example 3 A method for preparing a recyclable polyimide separator includes the following steps: First, visible impurities in the waste polyimide film were removed by ultrasonic cleaning in an ethanol solution for 45 min, followed by rinsing with deionized water and drying. The pretreated film was then immersed in a 3 mol / L lithium hydroxide solution at 40 °C for 50 h. Afterward, the film was rinsed with deionized water and washed in a 3 mol / L oxalic acid solution. It was then rinsed again with deionized water until the pH was near neutral, dried, and dissolved in tetrahydrofuran to obtain a polyamic acid solution with a viscosity of 1.0 Pa·s and a solid content of 35 wt%. This solution was then used to prepare a polyamic acid nanofiber membrane via centrifugal spinning. The membrane was pretreated at 200 °C for 45 min, then immersed in N,N-dimethylacetamide for 180 s, and finally imidized at 350 °C for 60 min to obtain a recycled polyimide membrane.

[0048] Example 4 A method for preparing a recyclable polyimide separator includes the following steps: First, visible impurities in the waste polyimide film were removed by ultrasonic cleaning in methanol solution for 50 min, followed by rinsing with deionized water and drying. The pretreated film was then immersed in a 0.2 mol / L hydrazine hydrate solution at 30 °C for 70 h. Afterward, the film was rinsed with deionized water and washed in a 0.2 mol / L perchloric acid solution. It was then rinsed again with deionized water until the pH was near neutral, dried, and dissolved in ethyl acetate to obtain a polyamic acid solution with a viscosity of 0.8 Pa·s and a solid content of 40 wt%. This solution was then used to prepare polyamic acid nanofiber membranes via electrospinning. The membranes were pretreated at 130 °C for 240 min, then immersed in methanol for 120 s, and finally imidized at 350 °C for 60 min to obtain a polyimide membrane.

[0049] Example 5 A method for preparing a recyclable polyimide separator includes the following steps: First, visible impurities in the waste polyimide film were removed by ultrasonic cleaning in an ethanol solution for 60 min, followed by rinsing with deionized water and drying. The pretreated film was then immersed in a 5 mol / L sodium hydroxide solution at 25 °C for 70 h. Afterward, the film was rinsed with deionized water and washed in a 5 mol / L hydrochloric acid solution. It was then rinsed again with deionized water until the pH was near neutral, dried, and dissolved in N-methyl-2-pyrrolidone to obtain a polyamic acid solution with a viscosity of 1.5 Pa·s and a solid content of 35 wt%. This solution was then used to prepare a polyamic acid nanofiber membrane via electrospinning. The membrane was pretreated at 100 °C for 300 min, then immersed in tetrahydrofuran for 200 s, and finally imidized at 300 °C for 120 min to obtain a polyimide membrane.

[0050] Comparative Example 1 Celgard 2500 commercially available diaphragm.

[0051] Comparative Example 2 A traditional two-step method for preparing polyimide separators involves dissolving equimolar amounts of 4,4-diaminodiphenyl ether and pyromellitic dianhydride in N,N-dimethylformamide to obtain a polyamic acid solution with a viscosity of 1.2 Pa·s and a solid content of 20 wt%. This solution is then electrospinned into polyamic acid nanofiber membranes, pretreated at 250°C for 10 min, immersed in tetrahydrofuran for 10 s, and finally imidized at 350°C for 120 min to obtain the polyimide separator.

[0052] The diaphragms obtained in Examples 1-5 and Comparative Example 2 were used to prepare samples, which were then tested using scanning electron microscopy (SEM). The results are as follows: Figure 1 As shown, it can be seen that there is no significant difference in the microstructure of the polyimide membranes recovered in each embodiment and the polyimide membranes prepared in Comparative Example 2.

[0053] Samples were prepared from the diaphragms obtained in Examples 1-5 and Comparative Example 2, and their results were subjected to total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Figure 2 As shown, the polyimide membranes recovered in each embodiment and the polyimide membrane prepared in Comparative Example 2 both exhibit a 1780 cm⁻¹ diameter. -1 (Asymmetrical) and 1708 cm -1 The absorption peak of the (symmetric) imide ring C=O, and at 1380 cm⁻¹ -1 The CN absorption peaks around the left and right confirm the successful preparation of the polyimide structure in the examples.

[0054] The separators obtained in Examples 1-5 and Comparative Example 2 were used to prepare samples, and their mechanical properties were tested. Symmetrical batteries were assembled using the separators obtained in Examples 1-5 and Comparative Examples 1-2, and relevant tests were performed. The ionic conductivity and lithium-ion transference number were calculated. The results are shown in Table 1.

[0055] Table 1. Comparison of membrane performance between Examples 1-5 and Comparative Examples 1-2

[0056] As can be seen from Table 1, the membranes obtained in the examples and the membranes prepared in Comparative Example 2 have excellent thermal stability, similar mechanical properties, and similar volume resistivity, both of which are significantly lower than the volume resistivity of Comparative Example 1, exhibiting higher ionic conductivity and lithium-ion transference number.

[0057] The above embodiments are merely illustrative of several implementations of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the invention patent. For those skilled in the art, any changes, modifications, substitutions, integrations, and parameter alterations to these embodiments without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A method for preparing a recyclable polyimide separator, characterized in that, Includes the following steps: Waste polyimide film is placed in an inorganic alkaline solution and soaked at 25-100℃ for 1-80 hours to obtain pretreated polyimide film; The pretreated polyimide film was washed with water until no alkaline residue remained on the surface, and then washed in an acid solution to obtain a deep-treated polyimide film. The deep-treated polyimide film was washed with water until no acid residue remained on the surface, dried, and then dissolved in a first organic solvent to obtain a polyamic acid solution. The polyamic acid solution was spun and dried to obtain a polyamic acid nanofiber membrane. The polyamic acid nanofiber membrane is treated at 100-250°C for 10-300 min, then treated in a second solvent for 10-200 s, the second solvent is removed, and then imidization is performed to obtain the recycled polyimide membrane. The first organic solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, and tetrahydrofuran; The second solvent includes at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, ethyl acetate, tetrahydrofuran, ethanol, water, and methanol.

2. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The waste polyimide film is placed in the inorganic alkaline solution, and the resulting pretreated polyimide film can be completely dissolved in the first organic solvent, which is the reaction endpoint.

3. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, At 30°C, the viscosity of the polyamic acid solution is 0.5-2.0 Pa·s.

4. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The concentration of the inorganic alkaline solution is 0.1-10 mol / L; the inorganic alkaline solution includes at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, lithium hydroxide, rubidium hydroxide, cesium hydroxide, sodium carbonate, potassium carbonate, ammonia, hydrazine hydrate, sodium phosphate, and potassium phosphate solution.

5. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The concentration of the acid solution is 0.1-10 mol / L; the acid solution includes at least one of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, and perchloric acid.

6. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The imidization temperature is 300-400℃, and the reaction time is 10-300 min.

7. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The spinning includes at least one of electrospinning and centrifugal spinning.

8. The method for preparing the recyclable polyimide membrane according to claim 1, characterized in that, The method also includes the following steps: removing visible impurities from the surface of the waste polyimide film, then ultrasonically cleaning it in an alcohol solution, followed by rinsing with deionized water, drying it, and then placing it in the inorganic alkaline solution; the alcohol solution includes at least one of ethanol solution and methanol solution.

9. A recyclable polyimide separator prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The tensile strength is 17-20 MPa, the volume resistivity is 2.96-3.27 ohms, and the ionic conductivity is 0.67-0.71 mS·cm. -1 The lithium-ion transference number is 0.43-0.

45.

10. A lithium-ion battery, characterized in that, This includes the recycled polyimide membrane prepared by the preparation method according to any one of claims 1 to 8.

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