High aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis and preparation method thereof

Abstract

The present invention provides a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis and a preparation method thereof. The preparation method of the composite film is as follows: S1. dissolving polyetherimide in a portion of N-methylpyrrolidone; S2. adding tetraethyl silicate to the solution obtained in S1 and dissolving it; S3. mixing hydrochloric acid and the remaining N-methylpyrrolidone and adding the resulting mixture to the solution obtained in S2 to react and obtain a SiO2 / PEI mixed solution; S4. electrospinning the SiO2 / PEI mixed solution to obtain a silica fiber / PEI polymer composite fiber mat; S5. drying and hot pressing the composite fiber mat to obtain a SiO2 fiber / polymer nanocomposite film. The in-situ preparation method solves the problem of difficult dispersibility of nanocomposites, and the obtained SiO2 fibers have a higher aspect ratio. The composite film has excellent high-temperature energy storage performance.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric composite materials, and in particular to a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis and a preparation method thereof Background Art

[0002] Dielectric capacitors offer advantages such as ultrafast charge and discharge speeds, extremely high power density, low losses, and high operating voltage. Over the past half century, they have been applied in fields such as inverters, high-power energy weapons, and high-frequency coupling circuits. However, their energy density remains far lower than that of energy storage devices such as lithium batteries and supercapacitors, significantly limiting their application in energy storage. Consequently, dielectric capacitors with high energy storage density have attracted widespread attention.

[0003] In the field of dielectric capacitors, ceramic capacitors have advantages such as smaller specific volume, higher dielectric constant, and high temperature resistance, but their low breakdown strength (E b ) and poor flexibility limit its application in the field of energy storage. Polymer-based film capacitors have gradually come to the stage of the times due to their high breakdown field strength, easy large-scale production, environmental protection, self-healing and other characteristics. Traditional film capacitors are cylindrical capacitors made by winding polymers and metal electrodes. In its upstream industry, polymer-based films are the key to determining the energy storage performance of capacitors. With the development of miniaturization of electronic devices, dielectric film materials with high energy storage density have become the focus of attention. In addition to energy storage density, thermodynamic stability has also become an important factor in the selection of materials in the field of dielectric energy storage. With the development of electronic technology, higher requirements are placed on the high temperature resistance of dielectric capacitors in many engineering fields. For example, the current new energy vehicles, oil and gas extraction, aerospace, high-power weapons and other fields require the operating temperature of materials to be greater than or close to 150°C. However, the dielectric film 1,2 biaxially oriented polypropylene (BOPP) currently widely used commercially has a low energy storage density (<5J / cm 3 ) and poor heat resistance (<105℃) cannot meet these requirements, so the research and development of dielectric materials that can work stably at high temperatures has attracted widespread attention.

[0004] Among the many high-temperature resistant polymer materials, polyimide (PI) and polyetherimide (PEI) containing aromatic heterocyclic structures have attracted widespread attention in the field of dielectric energy storage due to their good heat resistance, chemical stability, and excellent mechanical and electrical properties. However, for the Kapton film that has been widely used commercially, although the operating temperature is far below its glass transition temperature, its energy storage performance has dropped significantly and cannot meet the application requirements. For example, Kapton's energy storage performance drops from 1.53 J / cm at room temperature to 1.53 J / cm at room temperature. 3 The energy storage density and energy storage efficiency of 95.2% dropped sharply to 0.6 J / cm at 150 °C.3 The energy storage density and energy storage efficiency of 21.8% are due to the sharp increase in the conductivity loss of the material under high temperature and high electric field, and the sharp increase in conductivity. Too low energy storage efficiency will cause problems such as thermal runaway.

[0005] Therefore, in recent years, many studies have been conducted to suppress the conductivity of polymer dielectrics at high temperatures and high voltages, among which adjusting the energy level structure of the polymer is the main way to solve the problem. It is reported that the introduction of wide bandgap inorganic nanoparticles (20-50 nm) such as Al2O3, SiO2, HfO2, MgO and boron nitride into polymers to form dielectric polymer nanocomposites can significantly improve high-temperature energy storage performance. Among them, wide bandgap fillers will introduce deep traps and hinder thermally assisted charge transport under high voltage. On this basis, compared with nanoparticles, the introduction of nanofibers as fillers has better energy storage performance due to their ability to better hinder the breakdown path. However, most nanocomposites are currently prepared by solution blending, which brings some limitations. On the one hand, inorganic nanoparticles or fibers with high surface energy usually tend to agglomerate, resulting in poor uniformity of the film, which greatly limits the commercial preparation of inorganic / polymer composites. On the other hand, nanofibers prepared by solution blending usually have a shorter length and a larger diameter, that is, a lower aspect ratio, and almost no orientation, which is not conducive to obstructing and restricting the breakdown path. At the same time, this also leads to fewer interfaces, which is not conducive to the capture of carriers at high temperatures.

[0006] In summary, on the basis of ensuring good uniformity of composite materials, improving the high-temperature energy storage performance of materials through structural design of composite materials and optimization of energy level structure has become the focus and difficulty in the field of dielectric energy storage. Summary of the Invention

[0007] In order to solve the problems existing in the background technology, the present invention provides a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in situ synthesis and a preparation method thereof. The in situ preparation method combines the sol-gel reaction process of inorganic matter with the organic-inorganic composite process, and obtains a composite material of high aspect ratio nano-silica fiber and PEI polymer by electrospinning, which solves the problem of difficult dispersion of nano-composite materials prepared by traditional solution blending, and the obtained silica fiber has a higher aspect ratio.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in situ synthesis, comprising the following steps:

[0010] S1. Using N-methylpyrrolidone as a solvent, the polyetherimide was dissolved in part of N-methylpyrrolidone, heated and stirred until completely dissolved to obtain a polyetherimide solution;

[0011] S2. Tetraethyl silicate was added to the polyetherimide solution, heated with stirring until completely dissolved to obtain a tetraethyl silicate / polyetherimide mixed solution;

[0012] S3. The hydrochloric acid and the remaining N-methylpyrrolidone were mixed and added to the tetraethyl silicate / polyetherimide mixed solution to obtain the reaction solution, and the reaction was stirred for a certain time to obtain a SiO2 / PEI mixed solution;

[0013] S4. The SiO2 / PEI mixed solution in step S3 is electrospun to obtain a silica fiber / PEI polymer composite fiber felt;

[0014] S5. Drying and hot pressing the prepared silica fiber / PEI polymer composite fiber felt to obtain a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in situ synthesis.

[0015] According to the above scheme, based on 3 g of polyetherimide, the volume mass ratio of the tetraethyl silicate to the polyetherimide is 0.05-1 mL:3 g.

[0016] According to the above scheme, the amount of polyetherimide added is 25 g to 35 g based on 100 mL of N-methylpyrrolidone, and the portion of N-methylpyrrolidone added in step S1 accounts for 80% to 90% of the total N-methylpyrrolidone.

[0017] According to the above scheme, based on a hydrochloric acid concentration of 36% to 38%, the volume ratio of hydrochloric acid to the remaining N-methylpyrrolidone in step S3 is 5% to 10%, and the concentration of hydrochloric acid in the obtained reaction solution is 0.5% to 1%.

[0018] According to the above scheme, the stirring temperature in step S1 is 50-70° C. and the time is 12-16 h, and the stirring temperature in step S2 is 50-70° C. and the time is 4-5 h.

[0019] According to the above scheme, the reaction time in step S3 is 4 to 8 hours.

[0020] According to the above scheme, electrospinning is performed by high-speed directional spinning equipment in step S4. The specific steps are: injecting the SiO2 / PEI mixed solution into the syringe, then installing the syringe on the pushing device, sticking aluminum foil tape on the high-speed receiving roller, controlling the distance between the syringe and the high-speed fixed receiving roller to be 12.5-15 cm, applying a positive voltage of 12.5-16 kV to the syringe, applying a negative voltage of -3-4 kV to the high-speed receiving roller, and the syringe pushing speed is 0.08-1.2 mm / min.

[0021] According to the above scheme, in step S5, the film is removed after drying at 40-60°C for 12-24 hours, and then placed in a heat-resistant polyester film, preheated on a hot press for 5 minutes, hot-pressed at 210-225°C for 30-45 minutes, and cooled to obtain the high aspect ratio SiO2 fiber / polymer nanocomposite film based on in situ synthesis.

[0022] In a second aspect, the present invention provides a high aspect ratio SiO2 fiber / polymer nanocomposite film prepared by the above preparation method based on in-situ synthesis.

[0023] According to the above scheme, the content of SiO2 fibers in the composite film is 0.25 vol.% to 5 vol.%, the diameter is 20 to 300 nm, and the length is 1 to 100 μm.

[0024] The beneficial effects of the present invention are:

[0025] 1) The present invention cleverly combines the sol-gel reaction process of inorganic substances with the organic-inorganic composite process through an in-situ preparation method, and obtains a composite material of nano-silica fibers and PEI polymer with a high aspect ratio through electrospinning. This solves the problem of difficult dispersion of nano-composites prepared by traditional solution blending and shortens the preparation process steps. At the same time, because the silica fibers are formed in situ in the polymer during the electrospinning process, the obtained SiO2 fibers have better interaction with the PEI polymer, a higher aspect ratio, and parallel orientation;

[0026] 2) Compared with the traditional solution blending method for preparing inorganic / organic composite films, the present invention optimizes the chemical sol-gel process to achieve the first one-step method for preparing inorganic fiber / polymer dielectric films. It does not require high-temperature sintering or hydrothermal methods to prepare oxide inorganic materials, and does not require ultrasonic dispersion. Therefore, it is environmentally friendly and has the advantages of uniform preparation, while reducing preparation costs and having excellent commercial potential. It also provides new design ideas and technical solutions for inorganic / polymer nanocomposite functional films.

[0027] 3) The parallel-oriented nano-SiO2 fibers with high aspect ratio can effectively suppress the breakdown path and significantly increase the breakdown field strength of the composite film, thereby achieving an increase in energy storage density. The nano-SiO2 fibers with high aspect ratio introduce more inorganic / organic interfaces, which are more conducive to capturing carriers generated at high temperatures, thereby achieving an increase in energy storage efficiency at high temperatures. The composite film prepared by the present invention has a thermal conductivity of 8.99 J / cm at 150°C and 200°C, respectively. 3 and 6.18 J / cm 3 The maximum energy storage density, as well as energy storage efficiencies of 91.8% and 89.4%, demonstrate excellent high-temperature energy storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The scanning electron microscope (SEM) images of the cross section of the SiO2 fiber / PEI nanocomposite film prepared in Examples 1-4 of the present invention are shown;

[0029] Figure 2 This is the EDS spectrum (Si element) of the cross section of the SiO2 fiber / PEI nanocomposite film prepared in Example 3 of the present invention;

[0030] Figure 3 TEM bright field image and STEM and corresponding EDS spectra (Si element) of the SiO2 fiber / PEI nanocomposite film prepared in Example 3 of the present invention; (a) is a TEM bright field image, (b) and (c) are STEM and corresponding EDS spectra (Si element);

[0031] Figure 4 The scanning electron microscope image and corresponding EDS spectrum (Si element) of the cross section of the SiO2 particle / PEI composite film prepared in Comparative Example 2 of the present invention;

[0032] Figure 5 The dielectric energy storage properties of the SiO2 fiber / PEI nanocomposite films prepared in Examples 1-4 of the present invention at 150°C and 200°C;

[0033] Figure 6 The dielectric energy storage properties of the pure PEI polymer and the SiO2 particle / PEI composite film prepared in Comparative Examples 1-2 of the present invention at 150°C and 200°C;

[0034] Figure 7 The leakage current density of the SiO2 fiber / PEI nanocomposite film prepared in Example 3 of the present invention, the pure PEI polymer prepared in Comparative Examples 1-2, and the SiO2 particle / PEI composite film varies with the electric field at 150°C and 200°C;

[0035] Figure 8 The mechanical property test results of the SiO2 fiber / PEI nanocomposite film prepared in Example 3 of the present invention, the pure PEI polymer and the SiO2 particle / PEI composite film prepared in Comparative Examples 1-2, where (a) is the stress-strain curve of the nanoindentation test, and (b) is the tensile stress-strain curve of the MTS test;

[0036] Figure 9 It is a structural schematic diagram of the electrospinning and hot pressing processes in the preparation method of the present invention. DETAILED DESCRIPTION

[0037] The principles and features of the present invention are described below with reference to the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0038] It should be noted that, in the description of the embodiments of this application, the term "some specific embodiments" means that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0039] Introducing inorganic nanofibers into polymers can improve the high-temperature energy storage performance of polymer film materials. However, on the one hand, nanofibers tend to agglomerate and disperse unevenly in polymers. On the other hand, the fibers are short and large in diameter, i.e., have a low aspect ratio, which seriously affects the performance of dielectric films. In the present invention, the inventors combine the inorganic sol-gel reaction process with the organic-inorganic composite process through an in-situ preparation method, and obtain a high-aspect-ratio SiO2 fiber / polymer nanocomposite film through electrospinning. This solves the problem of uneven dispersion of nanocomposite materials prepared by traditional solution blending, and gives the composite film good orientation and a high-aspect-ratio morphology, which greatly improves the material performance.

[0040] The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis of the present invention comprises the following steps:

[0041] S1. Using N-methylpyrrolidone as a solvent, the polyetherimide was dissolved in part of N-methylpyrrolidone, heated and stirred until completely dissolved to obtain a polyetherimide solution;

[0042] S2. Tetraethyl silicate was added to the polyetherimide solution, heated with stirring until completely dissolved to obtain a tetraethyl silicate / polyetherimide mixed solution;

[0043] S3. The hydrochloric acid and the remaining N-methylpyrrolidone were mixed and added to the tetraethyl silicate / polyetherimide mixed solution to obtain the reaction solution, and the reaction was stirred for a certain time to obtain a SiO2 / PEI mixed solution;

[0044] S4. The SiO2 / PEI mixed solution in step S3 is electrospun to obtain a silica fiber / PEI polymer composite fiber felt;

[0045] S5. Drying and hot pressing the prepared silica fiber / PEI polymer composite fiber felt to obtain a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in situ synthesis.

[0046] Under the catalytic action of hydrochloric acid, the sol-gel reaction of tetraethyl silicate is carried out in a high concentration N-methylpyrrolidone solution of polyetherimide using the sol-gel principle, and silica colloids are generated in situ in the organic polymer. The polyetherimide solution with silica colloids uniformly dispersed in situ is then electrospun, and hot-pressed under conditions above the melting point of polyetherimide to obtain SiO2 fiber / polymer nanocomposite film. The schematic diagram of electrospinning is shown in FIG. Figure 9 shown.

[0047] In some specific embodiments, based on 3 g of polyetherimide, the volume mass ratio of tetraethyl silicate to polyetherimide is 0.05-1 mL:3 g.

[0048] Based on 3 g of polyimide, if the amount of tetraethyl silicate exceeds 1 mL, too much silica colloid will be generated by the sol-gel reaction, and the content of silica colloid in the polyetherimide solution will be too high, so silica fibers cannot be obtained by electrospinning.

[0049] In some specific embodiments, based on 100 mL of N-methylpyrrolidone, the amount of polyetherimide added is 25 g to 35 g, and the portion of N-methylpyrrolidone added in step S1 accounts for 80% to 90% of the total N-methylpyrrolidone.

[0050] In some specific embodiments, based on a hydrochloric acid concentration of 36% to 38%, the volume ratio of the hydrochloric acid to the remaining N-methylpyrrolidone in step S3 is 5% to 10%, and the concentration of the hydrochloric acid in the obtained reaction solution is 0.5% to 1%.

[0051] In some specific embodiments, the stirring temperature in step S1 is 50-70° C. and the stirring time is 12-16 h, and the stirring temperature in step S2 is 50-70° C. and the stirring time is 4-5 h.

[0052] In some specific embodiments, the reaction time in step S3 is 4 to 8 hours.

[0053] In some specific embodiments, in step S4, electrospinning is performed by a high-speed directional spinning device, and the specific steps are: injecting the SiO2 / PEI mixed solution into a syringe, then installing the syringe on a pushing device, sticking aluminum foil tape on a high-speed receiving roller, controlling the distance between the syringe and the high-speed fixed receiving roller to be 12.5 to 15 cm, applying a positive voltage of 12.5 to 16 kV to the syringe, applying a negative voltage of -3 to -4 kV to the high-speed receiving roller, and the syringe pushing speed is 0.08 to 1.2 mm / min.

[0054] In some specific embodiments, in step S5, after drying at 40-60°C for 12-24 hours, the film is peeled off and then placed in a heat-resistant polyester film, preheated on a hot press for 5 minutes, hot-pressed at 210-225°C for 30-45 minutes, and cooled to obtain the SiO2 fiber / polymer nanocomposite film.

[0055] The present invention also provides a SiO2 fiber / polymer nanocomposite film prepared by the above preparation method.

[0056] In the above preparation method, the volume mass ratio of tetraethyl silicate to polyetherimide is 0.05~1mL:3g. Based on the complete generation of silica from tetraethyl silicate, the volume content of silica in the SiO2 fiber / polymer nanocomposite film obtained by conversion based on mass and density is 0.25%~5%.

[0057] The volume fraction of SiO2 is calculated by the volume of tetraethyl silicate (TEOS) added, where the density of each component is as follows: PEI =1.3g / cm3,ρ TEOS =0.9g / cm3, .M TEoS and are the molecular weights of TEOS and SiO2, V TEOS is the volume of TEOS added, m PEI is the mass of added PEI.

[0058]

[0059] According to the above scheme, the content of the silica fiber in the composite film is 0.25 vol.% to 5 vol.%, the diameter is 20 to 300 nm, and the length is 1 to 100 μm.

[0060] Based on the above embodiments, the present invention is further described in the following specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. Experimental methods in the following examples, where specific conditions are not specified, generally follow the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by mass.

[0061] Example 1 Preparation of 0.5 vol.% SiO2 fiber / polymer nanocomposite film

[0062] 1) Place 8 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 70°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0063] 2) Add 0.1 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0064] 3) Mix 0.15 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0065] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0066] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, and hot-pressed at 220° C. for 30 min on a hot press. The film was then cooled to room temperature while maintaining the pressure to obtain the 0.5 vol.% SiO2 nanocomposite film.

[0067] Example 2 Preparation of 1 vol.% SiO2 fiber / PEI composite film

[0068] 1) Place 8 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 70°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0069] 2) Add 0.2 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0070] 3) Mix 0.15 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0071] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0072] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, and hot-pressed at 220° C. for 30 min on a hot press. The pressure was maintained and the temperature was lowered to room temperature to obtain the 1 vol.% SiO2 fiber / PEI nanocomposite film.

[0073] Example 3 Preparation of 1.5 vol.% SiO2 fiber / PEI composite film

[0074] 1) Place 8 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 70°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0075] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0076] 3) Mix 0.15 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0077] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0078] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, and hot-pressed at 220° C. for 30 min on a hot press. The pressure was maintained and the temperature was lowered to room temperature to obtain the 1.5 vol.% SiO2 fiber / PEI composite film.

[0079] Example 4 Preparation of 2 vol.% SiO2 fiber / PEI composite film:

[0080] 1) Place 8 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 70°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0081] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0082] 3) Mix 0.15 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0083] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0084] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, and hot-pressed at 220° C. for 30 min on a hot press. The pressure was maintained and the temperature was lowered to room temperature to obtain the 2 vol.% SiO2 fiber / PEI nanocomposite film.

[0085] Example 5 Preparation of 1.5 vol.% SiO2 fiber / PEI composite film (changing NMP concentration):

[0086] 1) Place 11.5 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 60°C and 600 rpm for 15 hours until the solution becomes transparent and pale yellow.

[0087] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 70° C. and stir for 4 h.

[0088] 3) Mix 0.25 ml of concentrated hydrochloric acid and 2.5 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0089] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0090] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, hot-pressed at 210° C. for 45 min on a hot press, and cooled to room temperature while maintaining the pressure to obtain the SiO 2 fiber / PEI nanocomposite film.

[0091] Example 6 Preparation of 1.5 vol.% SiO2 fiber / PEI composite film (changing spinning voltage):

[0092] 1) Place 10 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 55°C and 600 rpm for 16 hours until the solution becomes transparent and pale yellow.

[0093] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 50° C. and stir for 5 h.

[0094] 3) Mix 0.2 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0095] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 16 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0096] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, hot-pressed at 225° C. for 30 min on a hot press, and cooled to room temperature while maintaining the pressure to obtain the SiO 2 fiber / PEI nanocomposite film.

[0097] Example 7 Preparation of 1.5 vol.% SiO2 fiber / PEI composite film (changing spinning voltage):

[0098] 1) Place 10 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 52°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0099] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0100] 3) Mix 0.2 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0101] 4) The SiO2 / PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 10 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a composite fiber mat was obtained.

[0102] 5) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, hot-pressed at 215° C. for 30 min on a hot press, and then cooled to room temperature while maintaining the pressure to obtain the SiO 2 fiber / PEI nanocomposite film.

[0103] Comparative Example 1 Preparation of pure PEI film

[0104] 1) 8 ml of N-methylpyrrolidone (NMP) solution was placed in a 20 ml reagent bottle equipped with a magnet. 3 g of PEI particles were accurately weighed using an electronic balance. The bottle mouth was sealed with film to isolate it from moisture. The solution was then placed on a magnetic stirrer at 70°C and 600 rpm. Stir for 12 h until the solution became transparent and light yellow, thereby obtaining a PEI solution.

[0105] 2) The PEI mixed solution was injected into a syringe for electrospinning. The syringe was then mounted on a pusher. A high-speed receiving roller was taped with aluminum foil. The distance between the syringe and the high-speed receiving roller was maintained at 12.5 cm. A positive voltage of 12.5 kV was applied to the syringe, and a negative voltage of -3 kV was applied to the high-speed receiving roller. The syringe was pushed at a speed of 0.08 mm / min. After spinning for 1 hour, a fiber mat was obtained.

[0106] 3) The obtained fiber felt was dried at 60° C. for 12 h, then placed in a heat-resistant polyester film, and hot-pressed at 220° C. for 30 min on a hot press. The film was then cooled to room temperature while maintaining the pressure to obtain the pure PEI film.

[0107] Comparative Example 2 SiO2 particles / PEI composite film

[0108] 1) Place 8 ml of N-methylpyrrolidone (NMP) solution into a 20 ml reagent bottle equipped with a magnet. Accurately weigh 3 g of PEI particles using an electronic balance. Wrap the bottle mouth with a sealing film to isolate it from moisture. Place the solution on a magnetic stirrer at 70°C and 600 rpm for 12 hours until the solution becomes transparent and pale yellow.

[0109] 2) Add 0.3 ml of tetraethyl silicate to the PEI solution. Set the stirrer temperature to 60° C. and stir for 5 h.

[0110] 3) Mix 0.15 ml of concentrated hydrochloric acid and 2 ml of NMP, add the mixture to the solution prepared in 2), and continue stirring at room temperature for 4 h to obtain a SiO2 / PEI mixed solution.

[0111] 4) The above-mentioned SiO2 / PEI mixed solution is cast by a scraper, and the composite film obtained by casting is dried at 60°C for 12 hours, placed in a heat-resistant polyester film, and hot-pressed at 220°C on a hot press for 30 minutes. The pressure is maintained and the temperature is lowered to room temperature to obtain the SiO2 particle / PEI composite film.

[0112] The cross-sectional morphology of SiO2 fiber / PEI nanocomposite films with different volume fractions (0.5 vol.% to 2 vol.%) prepared in Examples 1, 2, 3, and 4 is shown in FIG. Figure 1 As shown, corresponding to Figure 1 (a), (b), (c) and (d) in Figure 2 The EDS spectrum of Si element in the cross section of SiO2 fiber / PEI nanocomposite film of Example 3 clearly shows that high aspect ratio silica fibers with a length of 10 to 30 μm and a diameter of 100 to 200 nm are evenly distributed in the polymer film with good density. As the volume fraction of added silica increases, the silica fibers become more obvious in the polymer composite film. Figure 3 The TEM and STEM characterization of the SiO2 fiber / PEI nanocomposite film of Example 3 further confirmed the in-situ formation of silica fibers in the polymer film and the extremely high aspect ratio. Figure 4The cross-sectional structure and EDS spectrum of the SiO2 particle / PEI composite film prepared by only the casting process in Comparative Example 2 are shown, indicating that one-dimensional SiO2 fibers cannot be obtained without the electrospinning process, and only traditional naturally grown SiO2 particles can be obtained.

[0113] Copper electrodes were plated on both sides of the SiO2 fiber / PEI nanocomposite films prepared in Examples 1 to 4, the pure PEI films prepared in Comparative Examples 1 and 2, and the SiO2 particle / PEI composite films. The following tests were then performed in a ferroelectric testing system: 1) hysteresis loop test to calculate the energy storage density and charge and discharge efficiency; 2) leakage current test, and a jump conduction model was fitted to obtain the leakage current.

[0114] Energy storage density and charge and discharge efficiency such as Figure 5 and 6 As shown in Figure 1, at a high temperature of 150°C, the breakdown field strength of the pure PEI film of Comparative Example 1 is 450 kV / mm and the energy storage density is 3.24 J / cm -3 , with an energy storage efficiency of 89.9%. The breakdown field strength of the SiO2 particle / PEI composite film of Comparative Example 2 is 525 kV / mm, and the energy storage density is 4.70 J / cm -3 , with an energy storage efficiency of 95.1%. Compared with the pure PEI film obtained in Comparative Example 1 and the SiO2 particle / PEI composite film obtained in Comparative Example 2, the breakdown field strength and energy storage density of the composite films prepared in Examples 1 to 4 are significantly improved with the introduction of high aspect ratio silica fibers. Among them, the energy storage density of the 1.5 vol.% film in Example 3 is most significantly improved, with a breakdown field strength of 730 kV / mm and an energy storage density of 8.99 J / cm -3 , and has an energy storage efficiency of 91.8%, showing ultra-high high-temperature energy storage performance. At a high temperature of 200°C, the breakdown field strength of the pure PEI film of Comparative Example 1 is 400kV / mm, and the energy storage density is 2.64J / cm -3 , with an energy storage efficiency of 89.4%. The breakdown field strength of the SiO2 particle / PEI composite film of Comparative Example 2 is 500 kV / mm, and the energy storage density is 3.91 J / cm -3 , with an energy storage efficiency of 90.4%. Examples 1 to 4 also exhibit ultra-high high-temperature energy storage performance, and their performance change trends are similar to those at 150°C. The breakdown field strength and energy storage efficiency have been greatly improved, and in Example 3, the highest energy storage density of 6.18 J / cm is achieved at a silica fiber content of 1.5 vol.%. -3 The results show that the prepared high aspect ratio SiO2 fiber / PEI nanocomposite film has excellent high temperature energy storage performance.

[0115] The leakage currents of the SiO2 fiber / PEI nanocomposite film prepared in Example 3, the pure PEI film prepared in Comparative Examples 1 and 2, and the SiO2 particle / PEI composite film at 150°C and 200°C are shown in FIG. Figure 7 As shown, the SiO2 fiber / polymer nanocomposite film prepared in Example 3 has significantly lower leakage current at 150°C and 200°C compared to Comparative Examples 1 and 2. Further fitting using the hopping conduction model shows that the SiO2 fiber / PEI composite film has the smallest hopping conduction distance, proving that the high aspect ratio silica fibers formed in situ in the SiO2 fiber / PEI nanocomposite film can more effectively introduce traps and suppress the migration of thermally excited carriers compared to particles. This further proves that the high aspect ratio SiO2 fiber / polymer nanocomposite film prepared in situ has extremely excellent high-temperature dielectric energy storage performance and has good application prospects in the field of high-temperature film capacitors.

[0116] The mechanical properties of the SiO2 fiber / PEI nanocomposite film prepared in Example 3 and the films prepared in Comparative Examples 1 and 2 were tested. Figure 8 As shown in the figure, the out-of-plane direction ( Figure 8 a) and in-plane direction ( Figure 8 b) stress-strain curve and calculate its corresponding Young's modulus. Compared with Comparative Example 1 (pure PEI film, Young's modulus is 4.1GPa and 1.9GPa) and Comparative Example 2 (SiO2 particles / PEI composite film, Young's modulus is 4.62GPa and 2.47GPa), SiO2 fiber / PEI nanocomposite film shows a higher Young's modulus in both the in-plane and out-of-plane directions, reaching 5.19GPa and 2.88GPa respectively. This is mainly attributed to the presence of high specific surface area and well-oriented SiO2 fibers in the composite film, which significantly improves the mechanical properties. In addition, the composite film with higher mechanical properties can effectively suppress electromechanical breakdown, thereby helping to improve the breakdown field strength, which further verifies the excellent electrical properties of high aspect ratio silica fiber / polymer nanocomposite materials.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis, characterized in that: The steps include: S1. Using N-methylpyrrolidone as a solvent, the polyetherimide was dissolved in part of N-methylpyrrolidone, heated and stirred until completely dissolved to obtain a polyetherimide solution; S2. Tetraethyl silicate was added to the polyetherimide solution, heated with stirring until completely dissolved to obtain a tetraethyl silicate / polyetherimide mixed solution; S3. The hydrochloric acid and the remaining N-methylpyrrolidone were mixed and added to the tetraethyl silicate / polyetherimide mixed solution to obtain the reaction solution, and the reaction was stirred for a certain time to obtain a SiO2 / PEI mixed solution; S4. The SiO2 / PEI mixed solution in step S3 is electrospun to obtain SiO2 fiber / PEI polymer composite fiber mat; S5. The prepared SiO2 fiber / PEI polymer composite fiber felt is dried and hot-pressed to obtain a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis.

2. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 1, characterized in that: Based on 3 g of polyetherimide, the volume mass ratio of the tetraethyl silicate to the polyetherimide is 0.05-1 mL:3 g.

3. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 1, characterized in that: Based on 100 mL of N-methylpyrrolidone, the amount of polyetherimide added is 25 g to 35 g, and the portion of N-methylpyrrolidone added in step S1 accounts for 80% to 90% of the total N-methylpyrrolidone.

4. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 1, characterized in that: Based on hydrochloric acid having a concentration of 36% to 38%, the volume ratio of hydrochloric acid to the remaining N-methylpyrrolidone in step S3 is 5% to 10%, and the concentration of hydrochloric acid in the obtained reaction solution is 0.5% to 1%.

5. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 1, characterized in that: The stirring temperature in step S1 is 50-70° C. and the stirring time is 12-16 hours. The stirring temperature in step S2 is 50-70° C. and the stirring time is 4-5 hours.

6. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 5, characterized in that: The reaction time in step S3 is 4 to 8 hours.

7. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to any one of claims 1 to 6, characterized in that: In step S4, electrospinning is performed using a high-speed directional spinning device. The specific steps are: injecting the SiO2 / PEI mixed solution into a syringe, then installing the syringe on a pushing device, sticking aluminum foil tape on a high-speed receiving roller, controlling the distance between the syringe and the high-speed fixed receiving roller to be 12.5 to 15 cm, applying a positive voltage of 12.5 to 16 kV to the syringe, applying a negative voltage of -3 to -4 kV to the high-speed receiving roller, and the syringe pushing speed is 0.08 to 1.2 mm / min.

8. The method for preparing a high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 1, characterized in that: In step S5, the film is removed after drying at 40-60°C for 12-24 hours, and then placed in a heat-resistant polyester film, preheated on a hot press for 5 minutes, hot-pressed at 210-225°C for 30-45 minutes, and cooled to room temperature to obtain the SiO2 fiber / polymer nanocomposite film.

9. A high aspect ratio SiO2 fiber / polymer nanocomposite film prepared by the preparation method according to any one of claims 1 to 8 based on in-situ synthesis.

10. The high aspect ratio SiO2 fiber / polymer nanocomposite film based on in-situ synthesis according to claim 9, characterized in that: The content of SiO2 fibers in the composite film is 0.25 vol.% to 5 vol.%, the diameter is 20 to 300 nm, and the length is 1 to 100 μm.

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