Modified polypropylene film and preparation method and application thereof, battery

Abstract

The present invention proposes a modified polypropylene film and a preparation method and application thereof, and a battery, and relates to the technical field of battery separators. The modified polypropylene film includes polypropylene and a modified copolymer, and the modified copolymer includes a product of a copolymerization reaction between polyethylene glycol and acrylamide. The technical solution of the present invention is to obtain a polypropylene film by modifying polypropylene with a modified copolymer to improve the performance of the modified polypropylene film, wherein the polyethylene glycol modification can fill the pores and defects in the polypropylene and improve the pore distribution; the acrylamide modification can promote the formation of a more stable grain boundary of polypropylene, reduce the defects at the grain boundary, improve the crystallinity of polypropylene, and thus improve the thermal stability of polypropylene; by copolymerizing polyethylene glycol and acrylamide to form a modified copolymer, a chemical cross-linking network can be formed to enhance the structural stability of the polymer, thereby improving its thermal stability.

Description

Technical Field

[0001] The invention relates to the technical field of battery separators, and in particular to a modified polypropylene film, a preparation method and application thereof, and a battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life and good safety. They are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptops and smart watches. The composition of lithium-ion batteries includes positive electrode, negative electrode, diaphragm and electrolyte. As one of the four major materials of lithium-ion batteries, the diaphragm does not participate in the electrochemical reaction in the battery, but it is a key internal component in the lithium battery. The key performance of the battery, such as capacity, cycle performance and charge and discharge current density, is directly related to the diaphragm. The safety of the diaphragm is an important factor affecting the safety of lithium-ion batteries.

[0003] Polypropylene (PP) has excellent mechanical properties, excellent corrosion resistance, electrical insulation, low density and low price, so it has become one of the most widely used plastics. Polypropylene diaphragms have many advantages, such as simple production and low cost, so they are widely used in many places, such as lithium-ion battery diaphragms, water environment purification, chemical refining industry and fabric industry.

[0004] The advantage of using polypropylene as a raw material for battery separators is that polypropylene has excellent mechanical properties, stable chemical properties, electrical insulation, and is low in price and easy to process, making it suitable for preparing separators, and there is no good solvent for polypropylene at room temperature.

[0005] However, the melting point of polypropylene film is low, and its heat resistance is poor when used as a battery separator. It is easy to shrink or melt in a high temperature environment, causing battery short circuit or failure. In addition, the pore size distribution of the polypropylene separator may be uneven, resulting in poor electrolyte penetration, affecting the battery's cycle performance and capacity. Summary of the invention

[0006] The main purpose of the present invention is to provide a modified polypropylene film and its preparation method and application, and a battery, aiming to improve the heat resistance and pore distribution of the polypropylene film.

[0007] To achieve the above object, the present invention provides a modified polypropylene film, wherein the modified polypropylene film comprises polypropylene and a modified copolymer, wherein the modified copolymer comprises a product of a copolymerization reaction between polyethylene glycol and acrylamide.

[0008] In one embodiment, the mass ratio of the polypropylene to the modified copolymer is 10:(2-4).

[0009] In one embodiment, the average molecular weight of the polyethylene glycol is 500 Da-2000 Da.

[0010] The present invention also provides a method for preparing a modified polypropylene film, comprising the following steps:

[0011] S10. The polyethylene glycol, acrylamide, an initiator, a crosslinking agent and an organic solvent are mixed, thermally initiated, a copolymerization reaction occurs, and the mixture is washed and dried to obtain a modified copolymer;

[0012] S20. Mix polypropylene with a non-polar solvent to obtain a first solution, mix the modified copolymer with a polar solvent to obtain a second solution, mix the first solution, the second solution and a surfactant, perform ultrasonic homogenization and drying, and perform hot pressing to obtain a modified polypropylene film.

[0013] In one embodiment, in step S10, the cross-linking agent includes N,N-methylenebisacrylamide; and / or,

[0014] In step S10, the initiator includes tetramethylethylenediamine; and / or,

[0015] In step S10, the organic solvent includes choline chloride.

[0016] In one embodiment, in step S10, the mass ratio of the polyethylene glycol to the acrylamide is 100:(1-20).

[0017] In one embodiment, in step S20, the polar solvent includes at least one of water, dimethyl sulfoxide and N,N-dimethylformamide; and / or,

[0018] In step S20, the non-polar solvent includes at least one of toluene, n-hexane, isooctane, dichloromethane and carbon tetrachloride; and / or,

[0019] In step S20, the surfactant includes at least one of sodium dodecylbenzene sulfonate, Tween 20 and polyvinyl alcohol.

[0020] In one embodiment, in step S20, the drying temperature is 105° C. to 150° C., and the drying time is 1 h to 2 h; and / or,

[0021] In step S20, the hot pressing temperature is 160°C to 170°C, the hot pressing pressure is 10 MPa to 30 MPa, and the hot pressing time is 5 min to 10 min.

[0022] The present invention also provides an application of a modified polypropylene film in the preparation of a battery separator, wherein the modified polypropylene film comprises the modified polypropylene film as described above, or a modified polypropylene film prepared by the preparation method of the modified polypropylene film as described above.

[0023] The present invention further provides a battery, the battery comprising a diaphragm, the diaphragm comprising the modified polypropylene film as described above, or a modified polypropylene film prepared by the method for preparing the modified polypropylene film as described above.

[0024] The technical solution of the present invention is to obtain a polypropylene film by modifying polypropylene with a modified copolymer to improve the performance of the modified polypropylene film, wherein polyethylene glycol is used for modification, and polyethylene glycol can fill the pores and defects in polypropylene to improve the pore distribution; acrylamide is used for modification, and acrylamide can promote polypropylene to form a more stable grain boundary, reduce defects at the grain boundary, improve the crystallinity of polypropylene, and thus improve the thermal stability of polypropylene; by copolymerizing polyethylene glycol and acrylamide to form a modified copolymer, a chemical cross-linking network can be formed, thereby limiting the movement of the polymer chain to enhance the structural stability of the polymer, thereby improving its thermal stability. In addition, the copolymer formed by polyethylene glycol and acrylamide can be used as a compatibilizer, playing a bridging role in the polypropylene matrix, improving the compatibility between polypropylene and the modified copolymer, thereby improving the overall performance of the modified polypropylene film. DETAILED DESCRIPTION

[0025] To make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0026] It should be noted that, in the embodiments, those without specifying specific conditions are carried out according to normal conditions or conditions recommended by the manufacturer. Those without specifying the manufacturer of reagents or instruments used are conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes, and "A and / or B" is taken as an example, including schemes A, B, or A and B that meet the same time. In addition, the technical schemes between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in the field to achieve. When the combination of the technical schemes is contradictory or cannot be achieved, it should be considered that the combination of such technical schemes does not exist, and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work, all belong to the scope of protection of the present invention.

[0027] At present, the melting point of polypropylene film is low, and its heat resistance is poor when used as a battery separator. It is easy to shrink or melt in a high temperature environment, causing battery short circuit or failure. In addition, the pore size distribution of the polypropylene separator may be uneven, resulting in poor electrolyte penetration, affecting the battery's cycle performance and capacity.

[0028] In view of this, the present invention provides a modified polypropylene film, wherein the modified polypropylene film comprises polypropylene and a modified copolymer, wherein the modified copolymer comprises a product of a copolymerization reaction between polyethylene glycol and acrylamide.

[0029] The technical solution of the present invention is to obtain a polypropylene film by modifying polypropylene with a modified copolymer to improve the performance of the modified polypropylene film, wherein polyethylene glycol is used for modification, and polyethylene glycol can fill the pores and defects in polypropylene to improve the pore distribution; acrylamide is used for modification, and acrylamide can promote polypropylene to form a more stable grain boundary, reduce defects at the grain boundary, improve the crystallinity of polypropylene, and thus improve the thermal stability of polypropylene; by copolymerizing polyethylene glycol and acrylamide to form a modified copolymer, a chemical cross-linking network can be formed, thereby limiting the movement of the polymer chain to enhance the structural stability of the polymer, thereby improving its thermal stability. In addition, the copolymer formed by polyethylene glycol and acrylamide can be used as a compatibilizer, playing a bridging role in the polypropylene matrix, improving the compatibility between polypropylene and the modified copolymer, thereby improving the overall performance of the modified polypropylene film.

[0030] In one embodiment, the mass ratio of the polypropylene to the modified copolymer is 10:(2-4).

[0031] The technical solution of the present invention improves the fluidity and processing performance of the polymer melt while ensuring the basic properties of the material by adjusting the mass ratio of polypropylene to the modified copolymer to 10: (2-4), making the material easier to shape and reducing energy consumption during the processing.

[0032] In one embodiment, the average molecular weight of the polyethylene glycol is 500 Da-2000 Da.

[0033] The technical solution of the present invention can dissolve quickly to improve the efficiency of the copolymerization reaction by using polyethylene glycol with an average molecular weight of 500 Da to 2000 Da. Preferably, in some embodiments of the present invention, the average molecular weight of polyethylene glycol is 2000 Da, which can form pores with a relatively uniform distribution; and polyethylene glycol with a molecular weight of 2000 Da generally has better thermal stability, which means that under high temperature environment, the pore structure of the diaphragm changes less, which is conducive to maintaining the stability of the pore distribution, thereby maintaining good ion conductivity.

[0034] The present invention also provides a method for preparing a modified polypropylene film, comprising the following steps:

[0035] S10. The polyethylene glycol, acrylamide, an initiator, a crosslinking agent and an organic solvent are mixed, thermally initiated, a copolymerization reaction occurs, and the mixture is washed and dried to obtain a modified copolymer;

[0036] S20. Mix polypropylene with a non-polar solvent to obtain a first solution, mix the modified copolymer with a polar solvent to obtain a second solution, mix the first solution, the second solution and a surfactant, perform ultrasonic homogenization and drying, and perform hot pressing to obtain a modified polypropylene film.

[0037] The technical solution of the present invention is to make polyethylene glycol, acrylamide, initiator and cross-linking agent copolymerize by thermal initiation to form a modified copolymer. This modified copolymer has a uniform molecular structure, can be better compatible with the polypropylene matrix, avoid the agglomeration phenomenon in the subsequent steps, and the modified copolymer produced by the cross-linking reaction helps to form a more compact network structure, increase the compactness of the membrane, and reduce the disorder of the pores; by mixing polypropylene with a non-polar solvent to form a first solution, and the modified copolymer is mixed with a polar solvent to form a second solution, and then adding a surfactant to mix, and then through ultrasonic homogenization treatment, the modified copolymer can be evenly dispersed in the polypropylene matrix, thereby enhancing the toughness of the membrane and reducing the possibility of brittle fracture; by hot pressing the mixture after ultrasonic homogenization, a uniform and consistent membrane structure can be obtained, which simplifies the processing flow and improves production efficiency. Further, the uniform pore structure and dense network are conducive to improving the ion conductivity of the membrane, and for applications as battery separators, the charge and discharge efficiency of the battery can be improved.

[0038] In one embodiment, in step S10, the cross-linking agent includes N,N-methylenebisacrylamide; and / or, in step S10, the initiator includes tetramethylethylenediamine; and / or, in step S10, the organic solvent includes choline chloride.

[0039] In the technical solution of the present invention, by using N,N-methylenebisacrylamide as a cross-linking agent, a stable three-dimensional network structure can be formed in the modified copolymer. The cross-linking agent can react with double bonds in acrylamide monomers to form cross-linking points, thereby increasing the cross-linking density of the copolymer. The increase in cross-linking density can significantly increase the mechanical strength and toughness of the modified copolymer, thereby making it difficult for the finally prepared modified polypropylene film to deform or break when subjected to external forces; by using tetramethylethylenediamine as an initiator, the polymerization reaction of polyacrylamide can be accelerated, the initiation efficiency can be improved, the reaction time can be shortened, and the polymerization reaction can be initiated under mild conditions, so that the reaction can be carried out at a lower temperature and pressure, thereby reducing energy consumption and production costs; by using choline chloride, a solution system for copolymerization reaction can be provided, and it is convenient to remove choline chloride in the subsequent reaction process.

[0040] In one embodiment, in step S10, the mass ratio of the polyethylene glycol to the acrylamide is 100:(1-20).

[0041] The technical solution of the present invention can form a relatively uniform pore structure in the copolymer by adjusting the mass ratio of polyethylene glycol to acrylamide to 100: (1-20), and these pores are large enough to allow lithium ions to pass through quickly, but not too large to cause a decrease in mechanical strength, thereby improving the ion conductivity of the diaphragm; since polyethylene glycol itself has good thermal stability, and the polyethylene glycol content is high at this mass ratio, it helps to improve the dimensional stability of the diaphragm under high temperature conditions, prevent the diaphragm from shrinking at high temperature, thereby avoiding short circuit caused by direct contact between the positive and negative electrodes.

[0042] In one embodiment, in step S20, the polar solvent includes at least one of water, dimethyl sulfoxide and N,N-dimethylformamide; and / or, in step S20, the non-polar solvent includes at least one of toluene, n-hexane, isooctane, dichloromethane and carbon tetrachloride; and / or, in step S20, the surfactant includes at least one of sodium dodecylbenzene sulfonate, Tween 20 and polyvinyl alcohol.

[0043] In the technical solution of the present invention, at least one of water, dimethyl sulfoxide and N,N-dimethylformamide is used as a polar solvent to dissolve the modified copolymer, so that the modified copolymer can be better dispersed in the solvent to form a uniform second solution; wherein dimethyl sulfoxide and N,N-dimethylformamide can be used not only as solvents but also as reaction media to promote the interaction between copolymer molecules, thereby facilitating the formation of a more uniform network structure; by using toluene, n-hexane, isooctane, dichloromethane or carbon tetrachloride as a non-polar solvent, the solubility of polypropylene in the solvent can be increased to form a stable first solution, thereby improving the uniformity of the final membrane material; by using sodium dodecylbenzene sulfonate, Tween 20 or polyvinyl alcohol as a surfactant, the dispersion uniformity of the first solution and the second solution during the mixing process can be improved.

[0044] In one embodiment, in step S20, the drying temperature is 105°C~150°C, and the drying time is 1 h~2 h; and / or, in step S20, the hot pressing temperature is 160°C~170°C, the hot pressing pressure is 10 MPa~30 MPa, and the hot pressing time is 5 min~10 min.

[0045] In the technical scheme of the present invention, by drying in the temperature range of 105°C to 150°C and with a drying time of 1 to 2 hours, the solvent can be effectively removed, ensuring that the solvent is completely volatilized in a short time without residual solvent, avoiding the degradation or instability of the membrane performance caused by residual solvent; appropriate drying temperature and time help to control the microstructure of the membrane, avoiding thermal degradation or other adverse changes of the membrane material due to excessive temperature or excessive time; by hot pressing in the temperature range of 160°C to 170°C, the molecular chains in the membrane material can be effectively rearranged, the density of the membrane can be improved, the porosity can be reduced, and the flatness of the membrane can be improved, and surface defects can be eliminated; by adjusting the hot pressing pressure between 10MPa and 30MPa, sufficient pressure can be applied to compact the membrane material tightly, thereby improving the mechanical strength of the membrane, including tensile strength, tear resistance, etc.; by controlling the hot pressing time to 5 to 10 minutes, the production rhythm can be accelerated, the production efficiency can be improved, the energy consumption can be reduced, and the production cost can be reduced.

[0046] The present invention also provides an application of a modified polypropylene film in the preparation of a battery separator, wherein the modified polypropylene film comprises the modified polypropylene film as described above, or a modified polypropylene film prepared by the preparation method of the modified polypropylene film as described above.

[0047] Since the present application adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0048] In the technical solution of the present invention, by applying the modified polypropylene film to the preparation of the battery separator, a battery separator with strong heat resistance and uniform pore distribution can be prepared. Good heat resistance means that in a high temperature environment, the separator can maintain its physical structure without deformation, melting or shrinkage, thereby maintaining a normal pore structure and size, ensuring the effective transmission of the electrolyte and preventing a short circuit between the positive and negative electrodes of the battery.

[0049] The present invention further provides a battery, the battery comprising a diaphragm, the diaphragm comprising the modified polypropylene film as described above, or a modified polypropylene film prepared by the method for preparing the modified polypropylene film as described above.

[0050] Since the present battery adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0051] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0052] Example 1

[0053] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0054] 1. Mix 10 g of polyethylene glycol 2000, 10 g of choline chloride, 2 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, react for 4 hours, let stand and cool, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0055] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 150°C for 1 hour, and hot press at 170°C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0056] Example 2

[0057] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0058] 1. Mix 10 g of polyethylene glycol 2000, 10 g of choline chloride, 0.1 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, react for 4 hours, let stand and cool, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0059] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 150°C for 1 hour, and hot press at 170°C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0060] Example 3

[0061] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0062] 1. Mix 10 g of polyethylene glycol 2000, 10 g of choline chloride, 2 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, react for 4 hours, let stand and cool, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0063] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 120°C for 90 minutes, and hot press at 165°C and 20 MPa for 10 minutes to obtain a modified polypropylene film.

[0064] Example 4

[0065] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0066] 1. Mix 10 g of polyethylene glycol 500, 10 g of choline chloride, 1 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, let stand and cool after 4 hours of reaction, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0067] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 3 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 150°C for 1 hour, and hot press at 170°C and 10 MPa for 10 minutes to obtain a modified polypropylene film.

[0068] Example 5

[0069] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0070] 1. Mix 10 g of polyethylene glycol 1000, 10 g of choline chloride, 2 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, let stand and cool after 4 hours of reaction, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0071] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, homogenize by ultrasonication, dry at 105°C for 2 hours, and hot press at 160°C and 30 MPa for 8 minutes to obtain a modified polypropylene film.

[0072] Example 6

[0073] This embodiment provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0074] 1. Mix 10 g of polyethylene glycol 2000, 10 g of choline chloride, 0.5 g of acrylamide, 0.05 g of N,N-methylenebisacrylamide and 0.02 g of tetramethylethylenediamine, heat to 60°C in a nitrogen atmosphere, heat-initiate copolymerization, react for 4 hours, let stand and cool, soak and wash with deionized water to remove choline chloride, and freeze-dry to obtain a modified copolymer;

[0075] 2. Take 10 g of polypropylene and dissolve it in dichloromethane, take 2 g of the modified copolymer and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 150°C for 1 hour, and hot press at 170°C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0076] Comparative Example 1

[0077] This comparative example provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0078] Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of polyethylene glycol 2000 and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, ultrasonically homogenize, dry at 150°C for 1 hour, and hot press at 170°C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0079] Comparative Example 2

[0080] This comparative example provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0081] Take 10 g of polypropylene and dissolve it in dichloromethane, take 4 g of acrylamide and dissolve it in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, homogenize by ultrasonication, dry at 150 °C for 1 hour, and hot press at 170 °C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0082] Comparative Example 3

[0083] This comparative example provides a modified polypropylene film, and the preparation method thereof comprises the following steps:

[0084] Take 10 g of polypropylene and dissolve it in dichloromethane, take 0.8 g of acrylamide and 3.2 g of polyethylene glycol 2000 and dissolve them in N,N-dimethylformamide, mix the two solutions with 5 g of sodium dodecylbenzene sulfonate, homogenize by ultrasonication, dry at 150 ° C for 1 hour, and hot press at 170 ° C and 30 MPa for 5 minutes to obtain a modified polypropylene film.

[0085] Performance Testing

[0086] Take the modified polypropylene films provided in Examples 1 to 6 and Comparative Examples 1 to 3, cut the films into 3 cm square samples and place them in a vacuum oven, and measure the thermal shrinkage of the modified polypropylene films after stabilizing at 200° C. for 30 minutes. The test results are shown in Table 1.

[0087] Table 1 Shrinkage of modified polypropylene films provided in Examples 1 to 6 and Comparative Examples 1 to 3

[0088]

[0089] According to Table 1, it can be seen that the shrinkage rates of the modified polypropylene films provided in Examples 1 to 6 after heat treatment are all within 40%, while the shrinkage rates of the modified polypropylene films provided in Comparative Examples 1 to 3 after heat treatment are all above 42%; wherein, Comparative Example 1 is a modified polypropylene film to which only polyethylene glycol 2000 is added as a modifying additive, and Comparative Example 2 is a modified polypropylene film to which only acrylamide is added as a modifying additive, and the heat shrinkage rates are 43.89% and 45.08% respectively, indicating that the single-component modifying additive has little effect on the heat resistance of the polypropylene film; and Comparative Example 3 provides a modified polypropylene film with uncross-linked polyethylene glycol 2000 and acrylamide as modifying additives, and the heat shrinkage rate thereof is 42.61%, which is lower than the heat shrinkage rates of the modified polypropylene films provided in Comparative Examples 1 and 2, indicating that when polyethylene glycol 2000 and acrylamide are added simultaneously, the heat resistance of the modified polypropylene film is more greatly affected. Compared with Comparative Example 3, the modified polypropylene films provided in Examples 1 to 6 have lower thermal shrinkage, indicating that the cross-linked polyethylene glycol 2000 and acrylamide further enhance the heat resistance of the polypropylene film, making it easier to be applied in the field of battery separators.

[0090] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A modified polypropylene film, characterized in that: The modified polypropylene film comprises polypropylene and a modified copolymer, wherein the modified copolymer comprises a product of a copolymerization reaction between N,N-methylenebisacrylamide and acrylamide; The mass ratio of the polypropylene to the modified copolymer is 10:(2-4); The preparation method of the modified polypropylene film comprises the following steps: S10. The polyethylene glycol, acrylamide, tetramethylethylenediamine, N,N-methylenebisacrylamide and choline chloride are mixed, thermally initiated, copolymerized, washed and dried to obtain a modified copolymer; S20. The polypropylene is mixed with a non-polar solvent to obtain a first solution, the modified copolymer is mixed with a polar solvent to obtain a second solution, the first solution, the second solution and a surfactant are mixed, ultrasonically homogenized and dried, and hot-pressed to obtain a modified polypropylene film; The mass ratio of the polyethylene glycol to the acrylamide is 100:(1-20).

2. The modified polypropylene film according to claim 1, characterized in that The average molecular weight of the polyethylene glycol is 500Da~2000Da.

3. A method for preparing a modified polypropylene film as claimed in claim 1 or 2, characterized in that: The following steps are involved: S10. The polyethylene glycol, acrylamide, tetramethylethylenediamine, N,N-methylenebisacrylamide and choline chloride are mixed, thermally initiated, copolymerized, washed and dried to obtain a modified copolymer; S20. Mix polypropylene with a non-polar solvent to obtain a first solution, mix the modified copolymer with a polar solvent to obtain a second solution, mix the first solution, the second solution and a surfactant, perform ultrasonic homogenization and drying, and perform hot pressing to obtain a modified polypropylene film.

4. The method for preparing a modified polypropylene film according to claim 3, characterized in that: In step S20, the polar solvent includes at least one of water, dimethyl sulfoxide and N,N-dimethylformamide; and / or, In step S20, the non-polar solvent includes at least one of toluene, n-hexane, isooctane, dichloromethane and carbon tetrachloride; and / or, In step S20, the surfactant includes at least one of sodium dodecylbenzene sulfonate, Tween 20 and polyvinyl alcohol.

5. The method for preparing a modified polypropylene film according to claim 3, characterized in that: In step S20, the drying temperature is 105°C to 150°C, and the drying time is 1 h to 2 h; and / or, In step S20, the temperature of hot pressing is 160° C. to 170° C., the pressure of hot pressing is 10 MPa to 30 MPa, and the duration of hot pressing is 5 min to 10 min.

6. Use of a modified polypropylene film in the preparation of a battery separator, characterized in that: The modified polypropylene film comprises the modified polypropylene film as claimed in any one of claims 1 to 2, or a modified polypropylene film prepared by the method for preparing a modified polypropylene film as claimed in any one of claims 3 to 5.

7. A battery, characterized in that: The battery comprises a diaphragm, and the diaphragm comprises the modified polypropylene film as claimed in any one of claims 1 to 2; or, a modified polypropylene film prepared by the method for preparing a modified polypropylene film as claimed in any one of claims 3 to 5.

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