A battery separator, method of making the same, and battery

Abstract

This invention relates to the field of battery technology, specifically disclosing a battery separator, its preparation method, and a battery. The battery separator comprises a triazine framework polymer membrane and a modified layer attached to the surface of the triazine framework polymer membrane. The modified layer is prepared from the following components by weight: 4-9 parts of nano-alumina, 6-11 parts of aqueous epoxy resin, and 0.3-0.6 parts of dispersant. The battery separator of this invention uses a triazine framework polymer membrane as the matrix, which can form pores through monomer polymerization, eliminating the need for complex melt extrusion stretching pore-forming processes, significantly simplifying the preparation process and reducing equipment investment costs. Simultaneously, the modified layer attached to the surface, composed of nano-alumina, aqueous epoxy resin, and dispersant, can significantly improve the electrolyte wettability and thermal stability of the separator, and impart good mechanical strength to the separator, thereby simultaneously solving the technical problems of complex processes, severe thermal shrinkage, and poor wettability in existing separators.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a battery separator, its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in consumer electronics, new energy vehicles, and energy storage due to their high energy density and long cycle life. The separator, as a core material of lithium-ion batteries, plays a crucial role in isolating the positive and negative electrodes and allowing lithium-ion transport; its performance directly determines the battery's safety and electrochemical performance.

[0003] Currently, commercially available membranes are mainly polyolefin microporous membranes, which are prepared by melt extrusion-stretching to form pores. However, they have significant drawbacks: the pore-forming process is complex and the equipment cost is high; the micropore uniformity is poor, which affects ion transport; the thermal stability is insufficient, and they are prone to shrinkage and short circuits at high temperatures; and the electrolyte wettability is poor, requiring additional modification. Summary of the Invention

[0004] Based on this, the purpose of this invention is to provide a battery separator, its preparation method, and a battery, which solves many defects of existing polyolefin separators, while providing a simple and cost-controllable preparation method to improve battery safety and electrochemical performance.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: The present invention first provides a battery separator, which includes a triazine framework polymer membrane and a modified layer attached to the surface of the triazine framework polymer membrane. The modified layer is prepared from the following components in parts by weight: 4-9 parts of nano alumina, 6-11 parts of waterborne epoxy resin, and 0.3-0.6 parts of dispersant.

[0006] The battery separator of this invention uses a triazine framework polymer membrane as the matrix, which can form pores through monomer polymerization, without the need for complex melt extrusion. The stretching and pore-forming process significantly simplifies the preparation process and reduces equipment investment costs. At the same time, the surface is coated with a modified layer composed of nano-alumina, water-based epoxy resin and dispersant, which can significantly improve the electrolyte wettability and thermal stability of the diaphragm and give the diaphragm good mechanical strength. This solves the technical problems of complex existing diaphragm processes, severe thermal shrinkage and poor wettability.

[0007] As a further improvement to the above-mentioned solution of the present invention, the battery separator has a thickness of 12~32μm, a porosity of 42%~62%, and a pore size of 0.4~0.7μm. This ensures that the separator has sufficient mechanical support and ion conductivity, avoiding the risk of increased internal resistance due to excessive thickness or short circuit risk due to excessive thinness. Simultaneously, it provides a uniform and unobstructed lithium-ion transport channel, which is beneficial for improving the rate performance and cycle stability of the battery.

[0008] As a further improvement to the above-mentioned solution of the present invention, the tensile strength of the battery separator is ≥18MPa. The tensile strength of the battery separator of the present invention reaches ≥18MPa, which is far superior to that of conventional polyolefin separators. This is due to the synergistic reinforcing effect of the triazine framework polymer matrix and the nano-alumina / epoxy resin modified layer, which makes the separator less prone to cracking, curling or puncture during battery assembly and charging / discharging, thus significantly improving the manufacturing yield and long-term reliability of the battery.

[0009] As a further improvement to the above-described scheme of the present invention, the triazine framework polymer is prepared by acid-catalyzed polymerization of 4,4'-dicyanobiphenyl monomer, and the number-average molecular weight of the triazine framework polymer is 5000~20000. Using 4,4'-dicyanobiphenyl monomer to prepare the triazine framework polymer by acid-catalyzed polymerization, and controlling its number-average molecular weight to be 5000~20000, on the one hand, can form a regular and rigid triazine network structure, giving the membrane excellent thermal stability and intrinsic microporous properties; on the other hand, the appropriate molecular weight range ensures a balance between film processability and mechanical properties, avoiding insufficient film strength due to excessively low molecular weight or processing difficulties due to excessively high molecular weight.

[0010] This invention also provides a method for preparing a battery separator as described above, comprising the following steps: dispersing nano-alumina, aqueous epoxy resin, and a dispersant in deionized water in a specific ratio to obtain a modified slurry with a solid content of 8% to 15%; coating the modified slurry onto both sides of a triazine framework polymer membrane and drying it to obtain the battery separator. The preparation method of this invention uses an aqueous slurry to directly coat both sides of a triazine framework polymer membrane, resulting in fewer process steps, simpler operation, no need for organic solvents, and environmental friendliness. By controlling the solid content to 8% to 15%, both the uniformity and adhesion of the coating are ensured, while avoiding coating defects caused by excessively thick or thin slurries. Continuous production can be achieved, effectively reducing manufacturing costs.

[0011] As a further improvement to the above-mentioned solution of the present invention, the dispersion is carried out by first stirring for 30 minutes, followed by ultrasonication at 300-500W for 40-70 minutes. This dispersion method of stirring followed by ultrasonication enables the nano-alumina to achieve uniform nanoscale dispersion in the waterborne epoxy resin, avoiding particle agglomeration. This ensures consistent synergistic effects among the components in the modified layer, ultimately resulting in a smooth, defect-free coating, which is beneficial for steadily improving the wettability and thermal stability of the diaphragm.

[0012] As a further improvement to the above-described scheme of the present invention, the areal density of the modified slurry coated on one side of the triazine framework polymer film is 1.2~3.2 g / m². 2The coating is performed using a microgravure coating method, and the drying is carried out at 70-85℃. The microgravure coating method enables high-precision, low-coating-weight uniform coating, while the drying temperature of 70-85℃ is gentle and efficient, avoiding high-temperature damage to the polymer membrane structure and ensuring the overall performance and batch stability of the diaphragm.

[0013] As a further improvement to the above-mentioned solution of the present invention, the preparation method of the triazine framework polymer membrane is as follows: Under ice bath conditions, an acid catalyst is added to the 4,4'-dicyanobiphenyl monomer, and after stirring for 15-30 minutes, the solution is transferred to a heating plate and heated under vacuum. After cooling to room temperature, the triazine framework polymer membrane is obtained. The reaction conditions are mild and the operation is safe. A self-supporting triazine framework polymer membrane can be obtained in one step, avoiding the complex processes of high-temperature melt extrusion and stretching in the preparation of traditional polyolefin separators, significantly shortening the process flow and reducing investment costs.

[0014] As a further improvement of the above-mentioned scheme of the present invention, the acid catalyst is composed of a mixture of trifluoromethanesulfonic acid and trifluoroacetic acid in a volume ratio of 1:1, and the molar ratio of the acid catalyst to the 4,4'-dicyanobiphenyl monomer is 1:3; the heating reaction is carried out at a temperature of 100°C for 2-3 hours.

[0015] The present invention also provides a battery comprising the battery separator as described above. The battery comprising the above-described battery separator possesses high safety, high rate performance, and long cycle life, making it particularly suitable for consumer electronics, new energy vehicles, and energy storage fields where safety and energy density requirements are stringent. Attached Figure Description

[0016] Figure 1 The infrared spectrum of the triazine framework polymer film in the battery separator prepared according to an embodiment of the present invention; Figure 2 The image shows the carbon NMR spectrum of the triazine framework polymer membrane in the battery separator prepared according to an embodiment of the present invention. Figure 3 This is a graph showing the carbon dioxide isothermal adsorption-desorption curve of the triazine framework polymer membrane in the battery separator prepared according to an embodiment of the present invention. Figure 4 This is a pore size distribution curve of the battery separator obtained in an embodiment of the present invention; Figure 5 The tensile strength diagram is shown for the battery separator obtained in an embodiment of the present invention. Figure 6 The diagram shows the cycle performance of the battery separator prepared according to the embodiments of the present invention and the commercial PE membrane. Detailed Implementation

[0017] To facilitate understanding of the present invention, a more comprehensive description will be given below with reference to specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0019] Example This embodiment proposes a battery separator, the preparation method of which is as follows: (1) Under ice bath conditions, the acid catalyst (obtained by mixing trifluoromethanesulfonic acid and trifluoroacetic acid in a volume ratio of 1:1) was added to the 4,4'-dicyanobiphenyl monomer and stirred for 20 min to form a viscous solution. The molar ratio of catalyst to monomer was 1:3. The solution was transferred to a heating plate equipped with a vacuum device at a temperature of 100°C. The reaction was allowed to stand for 2.5 h to remove the solvent. Heating was stopped, the polymer film was removed, and the membrane was peeled off at room temperature to obtain a triazine framework polymer membrane.

[0020] (2) By weight, 6 parts of nano-Al2O3, 8 parts of waterborne epoxy resin, and 0.4 parts of sodium polyacrylate were added to 85 parts of deionized water. After stirring for 30 min, the mixture was ultrasonicated at 400 W for 60 min to obtain a modified slurry. The modified slurry was then coated on both sides of the triazine framework polymer film (the surface density of the coating on one side was 2.2 g / m²) by a microgravure coating method. 2 After drying at 72℃ for 30 min, the battery separator was dried at 82℃ for 1.2 h to obtain a battery separator with a thickness of 22 μm.

[0021] The triazine framework polymer film prepared in this embodiment was characterized to obtain the following results: Figure 1 The infrared spectrum shown Figure 2 The shown is a carbon NMR spectrum. From... Figure 1 It can be seen that at 1508 and 1363 cm -1 The two strong absorption peaks correspond to the stretching and breathing vibration peaks of CN in the triazine framework unit. From Figure 2 It can be seen that the peak position of 172.0 ppm corresponds to the presence of carbon atom 'a' in the triazine ring, and the peak positions of 144.0 ppm, 135.5 ppm, 126.1 ppm, 120.0 ppm and 110.9 ppm correspond to the presence of hybrid carbon atoms (b, c, d and e) in the benzene ring, respectively.

[0022] The triazine framework polymer membrane prepared in this embodiment was subjected to isothermal adsorption-desorption of carbon dioxide: the sample was pre-dried under vacuum at 100°C for 12 hours, and then tested at 237.15 K in a CO2 atmosphere, as shown in the figure. Figure 3 The aforementioned curve graph. From Figure 3 It can be seen that the CO2 curve of the triazine framework polymer membrane prepared in this embodiment corresponds to a typical type I curve, indicating that it contains a large number of microporous structures.

[0023] The battery composite separator prepared in this embodiment was subjected to nitrogen isothermal adsorption-desorption: the sample was pre-dried under vacuum at 120°C for 24 hours, and then tested at 77.3 K in an N2 atmosphere to obtain the N2 adsorption isotherm curve. Based on the N2 adsorption isotherm curve, the pore size distribution curve of the battery separator prepared in this embodiment was calculated using density functional theory (DFT), as shown in the figure. Figure 4 As shown. From Figure 4 It can be seen that the pore size of the battery separator prepared in this embodiment is mainly distributed in the range of 0.4-0.7μm.

[0024] The battery separator prepared in this embodiment was subjected to a tensile test: the sample surface was wiped dry at room temperature, and then the mechanical properties of the battery separator were analyzed and tested at room temperature using a dynamic thermomechanical analyzer at a tensile rate of 1 N / min. The results are as follows. Figure 5 The tensile strength diagram shown is from... Figure 5 As can be seen, the tensile strength of the battery separator prepared in this embodiment is 26.37 MPa, and the elongation at break is 2.24%.

[0025] The battery separator prepared in this embodiment and a commercial PE microporous separator (thickness 20 μm, porosity 45%, tensile strength 12 MPa) were assembled into a battery with lithium iron phosphate (LFP) positive electrode, lithium metal negative electrode, and electrolyte (electrolyte is 0.5 mol / L LiPF6, solvent: EC, DMC, EMC mixed in a volume ratio of 1:1:1). (1) The battery was cycled 100 times at 10C, and the results are as follows. Figure 6 As shown; the results show that the battery assembled using the battery separator prepared in this embodiment has a capacity retention rate of 87.2% after 100 cycles at 10C, while the retention rate of commercial PE microporous membrane is only 77.5%. (2) The battery was subjected to a needle penetration test. The results show that the battery assembled using the battery separator prepared in this embodiment is safe in the needle penetration test, while the commercial PE microporous membrane short-circuit and catches fire when needled.

[0026] In summary, the battery separator of the present invention is significantly superior to commercial PE separators in terms of mechanical strength and battery performance, and has good application prospects.

[0027] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0028] The embodiments described above are merely illustrative 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 patent. 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 these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A battery separator, characterized in that, It includes a triazine framework polymer film and a modified layer attached to the surface of the triazine framework polymer film. The modified layer is prepared from the following components in parts by weight: 4-9 parts of nano-alumina, 6-11 parts of waterborne epoxy resin, and 0.3-0.6 parts of dispersant.

2. The battery separator according to claim 1, characterized in that, The battery separator has a thickness of 12~32μm, a porosity of 42%~62%, and a pore size of 0.4~0.7μm.

3. The battery separator according to claim 1, characterized in that, The tensile strength of the battery separator is ≥18MPa.

4. The battery separator according to claim 1, characterized in that, The triazine framework polymer is prepared by acid-catalyzed polymerization of 4,4'-dicyanobiphenyl monomer, and the number average molecular weight of the triazine framework polymer is 5000~20000.

5. A method for preparing a battery separator as described in any one of claims 1-4, characterized in that, It includes the following steps: Nano-alumina, waterborne epoxy resin, and dispersant are dispersed in deionized water in a certain proportion to obtain a modified slurry with a solid content of 8% to 15%. The modified slurry was coated on both sides of the triazine framework polymer membrane and dried to obtain the battery separator.

6. The method for preparing the battery separator according to claim 5, characterized in that, The dispersion is achieved by first stirring for 30 minutes, followed by ultrasonication at 300-500W for 40-70 minutes; the dispersant is a polycarboxylate or a fatty alcohol polyoxyethylene ether sulfate.

7. The method for preparing the battery separator according to claim 5, characterized in that, The modified slurry has a single-sided coating areal density of 1.2~3.2 g / m² on the triazine framework polymer film. 2 The coating is applied using a micro-recessed coating method, and the drying is carried out at 70~85℃.

8. The method for preparing the battery separator according to claim 5, characterized in that, The preparation method of the triazine framework polymer membrane is as follows: under ice bath, acid catalyst is added to 4,4'-dicyanobiphenyl monomer, stirred for 15-30 min, the solution is transferred to a heating plate and heated under vacuum, and then cooled to room temperature to obtain the triazine framework polymer membrane.

9. The method for preparing the battery separator according to claim 8, characterized in that, The acid catalyst is composed of a mixture of trifluoromethanesulfonic acid and trifluoroacetic acid in a volume ratio of 1:1, and the molar ratio of the acid catalyst to the 4,4'-dicyanobiphenyl monomer is 1:3; the heating reaction is carried out at a temperature of 100°C for 2-3 hours.

10. A battery, characterized in that, It includes the battery separator as described in any one of claims 1-4.

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