A lithium ion battery functional separator having a fiber network structure and a method of manufacturing the same

Abstract

This invention discloses a functional lithium-ion battery separator with a fiber network structure and its preparation method, belonging to the field of lithium-ion battery technology. The separator uses a polyolefin matrix as its base, with a three-dimensional continuous network framework composed of cyano-modified polymer nanofibers uniformly dispersed within it. The method involves blending the modified polymer nanofibers with a PE / PP matrix, followed by a casting process to uniformly disperse the nanofibers and form a fiber structure that penetrates the matrix. This invention alters the structure of traditional polyolefin membranes, integrating fiber formation and film formation processes, resulting in membranes that simultaneously possess high strength, low thermal shrinkage, and special properties imparted by the fiber's functionality. It is suitable for high-performance lithium-ion battery separators, and the process is easily scalable for mass production.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a functional separator for lithium-ion batteries with a fiber network structure and its preparation method. Background Technology

[0002] Polyolefin microporous membranes (such as polyethylene (PE), polypropylene (PP), and multilayer composite membranes) have become the mainstream material for lithium-ion battery separators due to their excellent electrochemical stability, suitable mechanical strength, and mature industrialization foundation. However, traditional polyolefin separators suffer from drawbacks such as insufficient heat resistance, poor wettability and electrolyte retention in polar electrolytes, and the need for further enhancement of mechanical strength. To overcome these performance bottlenecks, common modification strategies mainly include surface coating with heat-resistant layers, heat-resistant polymer blending, and modification through the introduction of composite inorganic fillers; however, their applications still face their respective limitations.

[0003] Constructing polymer fiber networks to reinforce the matrix is ​​an effective strategy for improving membrane performance. Typical approaches include pre-preparing nanofiber nonwoven fabrics and laminating them with polyolefins, or directly forming films via electrospinning. However, these methods have limitations such as complex processes and insufficient interlayer bonding. Therefore, there is an urgent need to develop novel composite membranes with novel structures, balanced performance, and ease of large-scale fabrication. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a functional lithium-ion battery separator with a three-dimensional fiber network framework and its preparation method. This separator achieves a synergistic improvement in mechanical properties, thermal dimensional stability, and electrolyte affinity by uniformly dispersing and constructing a continuous cyano-modified polymer nanofiber framework in a polyolefin matrix.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A functional lithium-ion battery separator with a fiber network structure includes: a polyolefin matrix and cyano-modified polymer nanofibers. The separator uses polyolefin as a continuous matrix and has a three-dimensional continuous network framework composed of cyano-modified polymer nanofibers uniformly dispersed inside.

[0006] In one embodiment, the polyolefin matrix is ​​one or more of polyethylene, polypropylene, or blends thereof.

[0007] In one embodiment, the cyano-modified polymer nanofibers are polymer nanofibers containing cyano functional groups, with a diameter ranging from 50 nm to 500 nm.

[0008] In one embodiment, the polymer containing cyano functional groups is polyacrylonitrile or a copolymer thereof.

[0009] In one embodiment, the cyano-modified polymer nanofibers account for 5% to 40% of the total mass of the membrane.

[0010] In one embodiment, the preparation method includes the following steps: (1) Preparation of cyano-modified polymer nanofiber dispersion; (2) Mix the polyolefin resin with the cyano-modified polymer nanofiber dispersion, heat and stir to form a uniform blend slurry; (3) Cast the blended slurry into a base film; (4) The base film is heat-set to obtain the diaphragm.

[0011] In one embodiment, in step (1), the cyano-modified polymer nanofiber dispersion is prepared by shearing, dispersing, homogenizing, or pre-spinning and then breaking the cyano-modified polymer nanofibers.

[0012] In one embodiment, in step (2), the heating temperature is higher than the melting point of the polyolefin resin.

[0013] In one embodiment, in step (3), the blended slurry is extruded and cast onto a cooling roller through a die head. The roller surface temperature is 10-30°C and the linear speed is 20-100 m / min, and the slurry is cooled to form a base film.

[0014] In one embodiment, in step (4), the base film is heat-set at 105-140°C for 5-15 minutes.

[0015] Compared with the prior art, the technical solution conceived in this application can achieve the following beneficial effects: (1) Structural innovation: This application pre-constructs functional cyano-modified nanofibers as a three-dimensional continuous framework in a polyolefin matrix, realizing the integration of membrane synthesis and fiber growth processes. The fiber framework not only plays a reinforcing role, but the cyano functional groups on its surface also endow the membrane with durable electrophilic properties.

[0016] (2) Excellent stability: The three-dimensional continuous nanofiber network of this application anchors the polyolefin matrix like "steel bars", which can effectively suppress its plastic flow and shrinkage at high temperatures. The polyolefin matrix provides high strength and toughness, while the uniformly dispersed nanofibers enhance the overall modulus of the material.

[0017] (3) Simple process: The preparation method of this application is based on the mature casting and stretching process. Functionalization can be achieved through simple blending modification without complicated coating or post-composite steps, and the production process is short. Attached Figure Description To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a SEM image of the separator prepared in Example 1 of the present application, which is a functional separator for lithium-ion batteries with a fiber network structure and its preparation method.

[0019] Figure 2 This is a sample cycle performance diagram of Example 1 of a lithium-ion battery functional separator with a fiber network structure and its preparation method according to this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0021] In one embodiment, this application provides a lithium-ion battery functional separator with a fiber network structure, comprising: a polyolefin matrix and cyano-modified polymer nanofibers. The separator uses a polyolefin as a continuous matrix, with a three-dimensional continuous network framework composed of uniformly dispersed cyano-modified polymer nanofibers inside. The polyolefin matrix is ​​one or more of polyethylene, polypropylene, or blends thereof, and the cyano-modified polymer nanofibers are polymer nanofibers containing cyano functional groups. The polymer containing cyano functional groups is polyacrylonitrile or a copolymer thereof.

[0022] In this embodiment, the present application provides a lithium-ion battery functional separator with a fiber network structure. A three-dimensional continuous nanofiber network is formed within a continuous polyolefin matrix. This fiber network anchors the polyolefin matrix like "steel bars," effectively suppressing its plastic flow and shrinkage at high temperatures. The polyolefin matrix provides high strength and high toughness, while the uniformly dispersed nanofibers enhance the overall modulus of the material.

[0023] In one embodiment, the preparation method includes the following steps: (1) Preparation of cyano-modified polymer nanofiber dispersion. The cyano-modified polymer nanofiber dispersion is prepared by shearing, dispersing, homogenizing or pre-spinning and then breaking the cyano-modified polymer nanofiber.

[0024] (2) Mix the polyolefin resin with the cyano-modified polymer nanofiber dispersion, heat and stir, and heat the mixture at a temperature higher than the melting point of the polyolefin resin to form a uniform blend slurry. (3) The blended slurry is cast into a base film. The blended slurry is extruded through a die and cast onto a cooling roller. The roller surface temperature is 10-30℃ and the linear speed is 20-100 m / min. The base film is then cooled.

[0025] (4) Heat-set the base film at 105-140℃ for 5-15 minutes to obtain the diaphragm.

[0026] In this embodiment, the preparation method provided by this application is based on a mature casting and stretching process. It can achieve functionalization with only simple blending modification, eliminating complex processes such as coating or post-composite bonding, significantly shortening the production process. The process is short, efficient, and conducive to large-scale production. Example

[0027] 1. Polyacrylonitrile was dissolved in N,N-dimethylformamide (DMF) to prepare an 8 wt% solution. A polyacrylonitrile (PAN) nanofiber dispersion (6% solid content) with an average diameter of about 120 nm and a length of about 50 μm was prepared by high pressure homogenization.

[0028] 2. Melt and mix 70g of polyethylene (PE) powder and the PAN nanofiber dispersion (equivalent to 10g of fiber mass) obtained in step 1 at 160°C for 2 hours to form a uniform slurry.

[0029] 3. Transfer the slurry to the casting device, and extrude it through the die onto a cooling roller at 25°C. The cooling roller has a linear speed of 80m / min to form a base film.

[0030] 4. Heat-set the base film at 125°C for 10 minutes, cool it, and then roll it up to obtain the final separator. Example

[0031] 1. Polyacrylonitrile was dissolved in DMF to prepare an 8 wt% solution, and a PAN nanofiber dispersion (6% solid content) with an average diameter of about 200 nm and a length of about 50 μm was prepared by high pressure homogenization.

[0032] 2. Melt and mix 70g of polyethylene (PE) powder and the PAN nanofiber dispersion (equivalent to 15g of fiber mass) obtained in step 1 at 190°C for 2 hours to form a uniform slurry.

[0033] 3. Transfer the slurry to the casting device, and extrude it through the die onto a cooling roller at 25°C. The cooling roller has a linear speed of 80m / min to form a base film.

[0034] 4. Heat-set the base film at 125°C for 10 minutes, cool it, and then roll it up to obtain the final separator. Example

[0035] 1. Polyacrylonitrile was dissolved in DMF to prepare a 10 wt% solution, and a PAN nanofiber dispersion (6% solid content) with an average diameter of about 350 nm and a length of about 50 μm was prepared by high pressure homogenization.

[0036] 2. Melt and mix 80g of polyethylene (PE) powder and the PAN nanofiber dispersion (equivalent to 25g of fiber mass) obtained in step 1 at 160°C for 2 hours to form a uniform slurry.

[0037] 3. Transfer the slurry to the casting device, and extrude it through the die onto a cooling roller at 25°C. The cooling roller has a linear speed of 80m / min to form a base film.

[0038] 4. Heat-set the base film at 110°C for 15 minutes, cool it, and then roll it up to obtain the final separator. Comparative Example 1 Pure PE membranes are prepared using a traditional wet process: PE is melted, extruded, cast, dried, and heat-set to obtain the PE membrane.

[0039] The above embodiments and comparative examples were subjected to performance tests: Characterization and test results 1. Physical and structural characterization The diaphragm in Example 1 was characterized by SEM as follows: Figure 1 As shown in the figure, the characterization results show that the diaphragm prepared in Example 1 has a three-dimensional continuous network fiber skeleton structure with an average fiber diameter of about 120 nm.

[0040] CR2032 coin cells were used for assembly and cycle performance testing. The positive electrode material was lithium iron phosphate, the electrolyte was lithium hexafluorophosphate dissolved in a carbonate mixture, and the separator was the sample prepared in Example 1. Before testing, the assembled cells were allowed to stand at room temperature for 12 hours. All electrochemical data were automatically recorded and analyzed by software, and the results are as follows: Figure 2 As shown, the specific capacity of the sample remained essentially unchanged after 100 cycles, but decreased by approximately 11.4% after 300 cycles, demonstrating excellent cycling performance.

[0041] The puncture strength and tensile strength of the samples were tested using an electronic universal testing machine according to GB / T 36363-2018. The measured properties are shown in Table 1.

[0042] Table 1. Diaphragm Performance Example 1 1.38 474 136 Example 2 1.46 469 131 Example 3 1.47 463 124 Comparative Example 1 1.93 449 122 The membrane prepared by this invention maintains good mechanical strength while exhibiting extremely low thermal shrinkage and significantly better electrolyte affinity than traditional PE membranes. This confirms the crucial role of the internal cyano-modified nanofiber network framework in enhancing the overall performance of the membrane.

[0043] The above description is merely a partial embodiment of the invention and does not constitute any limitation on this application. All raw material ratios, upper and lower limits of working conditions, and ranges in the preparation process of this application can achieve the desired results; therefore, specific embodiments are not listed here. Any person skilled in the art, without departing from the technical solution of this application, may make slight modifications or alterations to the above technical content to create equivalent embodiments of decorating. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application, without departing from the technical solution of this application, shall still fall within the scope of the technical solution of this application.

Claims

1. A functional separator for lithium-ion batteries with a fiber network structure, characterized in that, include: The membrane consists of a polyolefin matrix and cyano-modified polymer nanofibers. The polyolefin matrix is ​​a continuous matrix, and the cyano-modified polymer nanofibers are uniformly dispersed inside to form a three-dimensional continuous network framework.

2. The lithium-ion battery functional separator with a fiber network structure according to claim 1, characterized in that, The polyolefin matrix is ​​one or more of polyethylene, polypropylene, or blends thereof.

3. A lithium-ion battery functional separator with a fiber network structure according to claim 1, characterized in that, The cyano-modified polymer nanofibers are polymer nanofibers containing cyano functional groups, with a diameter range of 50 nm to 500 nm.

4. A lithium-ion battery functional separator with a fiber network structure according to claim 3, characterized in that, The polymer containing cyano functional groups is polyacrylonitrile or a copolymer thereof.

5. A lithium-ion battery functional separator with a fiber network structure according to claim 1, characterized in that, The cyano-modified polymer nanofibers account for 5% to 40% of the total mass of the membrane.

6. A lithium-ion battery functional separator with a fiber network structure according to any one of claims 1-5, characterized in that, Its preparation method includes the following steps: (1) Preparation of cyano-modified polymer nanofiber dispersion; (2) Mix the polyolefin resin with the cyano-modified polymer nanofiber dispersion, heat and stir to form a uniform blend slurry; (3) Cast the blended slurry into a base film; (4) The base film is heat-set to obtain the diaphragm.

7. The preparation method according to claim 6, characterized in that, In step (1), the cyano-modified polymer nanofiber dispersion is prepared by shearing, dispersing, homogenizing, or pre-spinning and then breaking the cyano-modified polymer nanofibers.

8. The preparation method according to claim 6, characterized in that, In step (2), the heating temperature is higher than the melting point of the polyolefin resin.

9. The preparation method according to claim 6, characterized in that, In step (3), the blended slurry is extruded and cast onto a cooling roller through a die head. The roller surface temperature is 10-30℃ and the linear speed is 20-100 m / min. The slurry is then cooled to form a base film.

10. The preparation method according to claim 6, characterized in that, In step (4), the base film is heat-set at 105-140°C for 5-15 minutes.

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