Fiber-woven structure dielectric film for high energy density capacitor and method of manufacturing the same

Abstract

The application provides a fiber weaving structure dielectric film for a high energy density capacitor and a preparation method, and aims at the fact that the dielectric constant and the breakdown strength of a polymer-based dielectric material are difficult to be simultaneously improved, so that the energy density cannot meet the demand of a high power density energy storage capacitor. A polyetherimide / polyvinylidene fluoride-hexafluoropropylene core-shell structure fiber with a core-shell structure is prepared through a coaxial electrospinning technology, a composite film is formed through laminated hot pressing, the weaving structure is adjusted by adjusting the core-shell fiber composition content, the fiber orientation stacking direction and the stacking layer number, the mechanical strength of the film is enhanced, carriers are captured by deep traps, the breakdown strength is significantly improved, the high dielectric constant is maintained by utilizing interface polarization, and the energy density is comprehensively improved.

Description

Technical Field

[0001] This invention belongs to the field of polymer dielectric materials for electrostatic capacitors, specifically relating to dielectric films for capacitors with high breakdown strength and high energy density, and their preparation methods. Background Technology

[0002] Dielectric film capacitors, with their ultrafast charging and discharging speeds and extremely high power densities, are widely used in hybrid electric vehicles, power transmission, and electromagnetic weapons as fundamental components of modern electronic and power systems, serving as important energy storage devices. However, the energy storage capacity of dielectric capacitors is far lower than that of electrochemical energy storage devices. Currently available commercial dielectric materials have relatively low dielectric constants (generally below 2.2), failing to meet the urgent demands for compactness, reliability, and efficiency in the capacitor field. Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFA) is a ferroelectric polymer dielectric material with relatively high dielectric constants (8–12), but these polymers also exhibit high polarization losses and insufficient breakdown electric field resistance. Polyetherimide is a linear polymer dielectric material with very low polarization losses, but its dielectric constant (~3.2) is slightly lower than that of ferroelectric polymers. Therefore, improving the breakdown strength of dielectric film materials used as capacitor energy storage media while maintaining a high dielectric constant is a key issue in achieving high energy density. Summary of the Invention

[0003] This invention addresses the challenge of simultaneously improving the dielectric constant and breakdown strength of polymer-based dielectric materials, which leads to insufficient energy density for high-power-density energy storage capacitors. It utilizes coaxial electrospinning technology to prepare core-shell polyetherimide / polyvinylidene fluoride-hexafluoropropylene core-shell structure fibers, which are then laminated and hot-pressed to form a composite film. By adjusting the composition, fiber orientation, and number of stacked layers, the braiding structure is controlled, enhancing the film's mechanical strength, creating deep traps to capture charge carriers, significantly improving breakdown strength, and maintaining a high dielectric constant through interfacial polarization, thus comprehensively improving energy density. Specifically:

[0004] 1. Significantly improves the breakdown strength of the dielectric of polyetherimide / polyvinylidene fluoride-hexafluoropropylene composite films;

[0005] 2. Improve the mechanical and dielectric properties of composite films to obtain energy storage dielectric materials that combine high energy density and high charge / discharge efficiency.

[0006] The technical solution adopted in this invention is as follows:

[0007] Polyetherimide / polyvinylidene fluoride-hexafluoropropylene composite films with a certain three-dimensional cross-woven structure were prepared by electrospinning and hot pressing processes. The detailed steps are as follows:

[0008] Step 1: Weigh a certain mass of polyvinylidene fluoride-hexafluoropropylene powder and place it in a beaker. Add N-methylpyrrolidone solvent and acetone in a 1:1 volume ratio to the beaker and stir at room temperature to obtain an outer layer precursor solution. By adjusting the mass of the polyvinylidene fluoride-hexafluoropropylene powder, a series of outer layer precursor solutions with different volume fractions can be obtained.

[0009] Step 2: Weigh a certain mass of polyetherimide particles and place them in a beaker. Add N-methylpyrrolidone solvent and acetone in a volume ratio of 9:8 to the beaker, and stir at 40°C to obtain an inner layer precursor solution. By adjusting the mass of the polyetherimide particles, a series of inner layer precursor solutions with different volume fractions can be obtained.

[0010] Step 3: Using two 10mL syringes, draw up the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of a specially designed coaxial spinning needle. Apply a high voltage of 16-18kV to initiate the electrospinning process. The speed of the spinning receiving shaft is 600 (±50) rpm. The ratio of the propulsion speed of the inner and outer layer solutions is consistent with the ratio of the inner and outer layer areas of the coaxial spinning needle. The product of the ratio of the volume concentration of polyetherimide in the inner layer precursor solution to the volume concentration of polyvinylidene fluoride-hexafluoropropylene in the outer layer precursor solution and the ratio of the inner and outer layer areas of the coaxial spinning needle is the volume ratio of polyetherimide to polyvinylidene fluoride-hexafluoropropylene in the obtained spun fiber.

[0011]

[0012] The ambient temperature during the entire electrospinning process is maintained at around 26℃, the humidity is between 10% RH and 30% RH, and the spinning time is between 12h and 18h.

[0013] Step 4: Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for more than 24 hours.

[0014] Step 5: Stack 2 to 3 layers of fiber felt in the same direction or perpendicularly in the same direction in the mold. Preheat the hot press to 190℃ for 30 minutes. Place the stacked fiber felt in the mold and maintain the pressure at 5MPa for 10 minutes, then release the pressure for 5 minutes to expel air. Next, apply pressure at 200℃ and 210℃ for 10 minutes each, then release the pressure for 5 minutes. Finally, apply a pressure of 7.5MPa at 220℃ for 1 hour, and cool with air to obtain composite films with different structures.

[0015] The advantages and beneficial effects of this invention are as follows:

[0016] 1. The breakdown strength of the three-dimensional cross-woven polyetherimide / polyvinylidene fluoride-hexafluoropropylene composite film can reach 737.5kV / mm, which is nearly 50kV / mm higher than that of the single-fiber polyetherimide / polyvinylidene fluoride-hexafluoropropylene composite film.

[0017] 2. The composite thin film exhibits excellent dielectric properties, with an energy storage density reaching 29.3 J / cm². 3 It is 1.5 times that of single-fiber oriented composite films, and its charge / discharge efficiency can reach over 70%. Attached Figure Description

[0018] Figure 1 This is a flowchart of the process of creating this invention.

[0019] Figure 2 It is a cross-sectional image of a three-dimensional woven composite film in the vertical direction.

[0020] Figure 3 The breakdown voltage Weibull distribution and characteristic breakdown strength of a three-dimensional braided composite film with a polyetherimide volume fraction of 10% are presented.

[0021] Figure 4 The discharge energy density of a three-dimensional woven composite film with a polyetherimide volume fraction of 10% under different electric fields.

[0022] Figure 5 The charge and discharge efficiency of a three-dimensional woven composite film with a polyetherimide volume fraction of 10% under different electric fields is measured.

[0023] Figure 6 It is a comparison of the highest breakdown strength and highest energy storage density of three composite films with different fiber structures. Detailed Implementation

[0024] To better clarify the technical solution of the present invention, it is now described in conjunction with the appendix. Figure 1-6 The following is a detailed explanation with specific examples:

[0025] Implementation Case 1:

[0026] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0027] (2) Weigh 1.8g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0028] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 23G / 17G coaxial spinning needle and apply a high voltage of 18kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 600 rpm. The propulsion speed of the inner and outer layer solutions is 0.5 μL / min and 6 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 30% RH throughout the electrospinning process. The spinning time is 18h.

[0029] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0030] (5) Place two layers of fiber felt stacked in the same direction in a mold. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain the pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, and depressurize for 5 minutes each. Finally, apply a pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a unidirectional composite film with a polyetherimide volume fraction of 5% is obtained.

[0031] Implementation Case 2:

[0032] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0033] (2) Weigh 1.8g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0034] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 23G / 17G coaxial spinning needle and apply a high voltage of 18kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 610 rpm. The propulsion speed of the inner and outer layer solutions is 0.5 μL / min and 6 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 30% RH throughout the electrospinning process. The spinning time is 18h.

[0035] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0036] (5) Place two layers of fiber felt in a mold, stacked perpendicularly. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, then depressurize for 5 minutes. Finally, apply pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a double-layer cross-structured composite film with a polyetherimide volume fraction of 5% is obtained.

[0037] Implementation Case 3:

[0038] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0039] (2) Weigh 1.8g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0040] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 23G / 17G coaxial spinning needle and apply a high voltage of 17.5kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 550 rpm. The propulsion speed of the inner and outer layer solutions is 0.5 μL / min and 6 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 20%RH throughout the electrospinning process. The spinning time is 15h.

[0041] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0042] (5) Three layers of fiber felt were stacked in a perpendicular direction and placed in a mold. The heating table of the hot press was preheated to 190°C for 30 minutes. After placing the stacked fiber felt in, it was held at 5 MPa for 10 minutes, and then the pressure was released for 5 minutes to allow air to escape. Then, the pressure was applied at 200°C and 210°C for 10 minutes each, and then the pressure was released for 5 minutes. Finally, a pressure of 7.5 MPa was applied at 220°C for 1 hour. After cooling with air blowing, a three-dimensional woven composite film with a polyetherimide volume fraction of 5% was obtained.

[0043] Implementation Case 4:

[0044] (1) Weigh 3.5g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0045] (2) Weigh 2.3g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0046] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 17kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 580 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 15% RH throughout the electrospinning process. The spinning time is 18h.

[0047] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0048] (5) Place two layers of fiber felt stacked in the same direction in a mold. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain the pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, and depressurize for 5 minutes each. Finally, apply a pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a unidirectional composite film with a polyetherimide volume fraction of 8% is obtained.

[0049] Implementation Case 5:

[0050] (1) Weigh 3.5g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0051] (2) Weigh 2.3g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0052] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 17kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 560 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 15% RH throughout the electrospinning process. The spinning time is 18h.

[0053] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0054] (5) Place two layers of fiber felt in a mold, stacked perpendicularly. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, then depressurize for 5 minutes. Finally, apply pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a double-layer cross-structured composite film with a polyetherimide volume fraction of 8% is obtained.

[0055] Implementation Case Six:

[0056] (1) Weigh 3.5g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0057] (2) Weigh 2.3g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0058] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 17kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 600 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 20% RH throughout the electrospinning process. The spinning time is 13h.

[0059] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0060] (5) Three layers of fiber felt were stacked in a perpendicular direction and placed in a mold. The heating table of the hot press was preheated to 190°C for 30 minutes. After placing the stacked fiber felt in, it was held at 5 MPa for 10 minutes, and then the pressure was released for 5 minutes to allow air to escape. Then, the pressure was applied at 200°C and 210°C for 10 minutes each, and then the pressure was released for 5 minutes. Finally, a pressure of 7.5 MPa was applied at 220°C for 1 hour. After cooling with air blowing, a three-dimensional woven composite film with a polyetherimide volume fraction of 8% was obtained.

[0061] Implementation Case Seven:

[0062] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0063] (2) Weigh 3.15g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0064] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 16.7kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 620 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 30% RH throughout the electrospinning process. The spinning time is 17h.

[0065] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0066] (5) Place two layers of fiber felt stacked in the same direction in a mold. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain the pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, and depressurize for 5 minutes each. Finally, apply a pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a unidirectional composite film with a polyetherimide volume fraction of 10% is obtained.

[0067] Implementation Case 8:

[0068] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0069] (2) Weigh 3.15g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0070] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 16kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 650 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 25% RH throughout the electrospinning process. The spinning time is 15h.

[0071] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0072] (5) Place two layers of fiber felt in a mold, stacked perpendicularly. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, then depressurize for 5 minutes. Finally, apply pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a double-layer cross-structured composite film with a polyetherimide volume fraction of 10% is obtained.

[0073] Implementation Case Nine:

[0074] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0075] (2) Weigh 3.15g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0076] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 22G / 17G coaxial spinning needle and apply a high voltage of 16kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 620 rpm. The propulsion speed of the inner and outer layer solutions is 1 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 20% RH throughout the electrospinning process. The spinning time is 13h.

[0077] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0078] (5) Three layers of fiber felt were stacked in a perpendicular direction and placed in a mold. The heating table of the hot press was preheated to 190°C for 30 minutes. After placing the stacked fiber felt in, it was held at 5 MPa for 10 minutes, and then the pressure was released for 5 minutes to allow air to escape. Then, the pressure was applied at 200°C and 210°C for 10 minutes each, and then the pressure was released for 5 minutes. Finally, a pressure of 7.5 MPa was applied at 220°C for 1 hour. After cooling with air blowing, a three-dimensional woven composite film with a polyetherimide volume fraction of 10% was obtained.

[0079] Implementation Case 10:

[0080] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0081] (2) Weigh 2.27g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0082] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 21G / 17G coaxial spinning needle and apply a high voltage of 17.4kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 590 rpm. The propulsion speed of the inner and outer layer solutions is 2 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 10% RH throughout the electrospinning process. The spinning time is 15h.

[0083] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0084] (5) Place two layers of fiber felt stacked in the same direction in a mold. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain the pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, and depressurize for 5 minutes each. Finally, apply a pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a unidirectional composite film with a polyetherimide volume fraction of 15% is obtained.

[0085] Implementation Case Eleven:

[0086] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0087] (2) Weigh 2.27g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0088] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 21G / 17G coaxial spinning needle and apply a high voltage of 17.4kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 600 rpm. The propulsion speed of the inner and outer layer solutions is 2 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 15% RH throughout the electrospinning process. The spinning time is 13h.

[0089] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0090] (5) Place two layers of fiber felt in a mold, stacked perpendicularly. Preheat the hot press to 190°C for 30 minutes. Place the stacked fiber felt in the mold and maintain pressure at 5 MPa for 10 minutes, then depressurize for 5 minutes to allow air to escape. Then pressurize at 200°C and 210°C for 10 minutes each, then depressurize for 5 minutes. Finally, apply pressure of 7.5 MPa at 220°C for 1 hour. After cooling with air blowing, a double-layer cross-structured composite film with a polyetherimide volume fraction of 15% is obtained.

[0091] Implementation Case Twelve:

[0092] (1) Weigh 3.6g of polyvinylidene fluoride-hexafluoropropylene powder and place it in a 50mL beaker. Add 8mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at room temperature for 24h to obtain the outer precursor solution.

[0093] (2) Weigh 2.27g of polyetherimide particles and place them in a 50mL beaker. Add 9mL of N-methylpyrrolidone solvent and 8mL of acetone to the beaker and stir at 40℃ for 12h to obtain the inner layer precursor solution.

[0094] (3) Use two 10mL syringes to draw the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the 21G / 17G coaxial spinning needle and apply a high voltage of 17kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 610 rpm. The propulsion speed of the inner and outer layer solutions is 2 μL / min and 9 μL / min respectively. The ambient temperature is maintained at 26℃ and the humidity is below 10% RH throughout the electrospinning process. The spinning time is 12h.

[0095] (4) Remove the prepared fiber felt from the aluminum foil, dry it in air at 120°C for 2 hours to remove excess solvent, and then dry it in a vacuum for 24 hours.

[0096] (5) Three layers of fiber felt were stacked in a perpendicular direction and placed in a mold. The heating table of the hot press was preheated to 190°C for 30 minutes. After placing the stacked fiber felt in, it was held at 5 MPa for 10 minutes, and then the pressure was released for 5 minutes to allow air to escape. Then, the pressure was applied at 200°C and 210°C for 10 minutes each, and then the pressure was released for 5 minutes. Finally, a pressure of 7.5 MPa was applied at 220°C for 1 hour. After cooling with air blowing, a three-dimensional woven composite film with a polyetherimide volume fraction of 15% was obtained.

[0097] The following is a comparison of the dielectric properties of the three-dimensional structure designed in this invention with other structures for samples of the same volume fraction:

[0098] Table 1

[0099] Breakthrough field strength 5% sample 8% of samples 10% of the samples 15% of samples One direction 621.5kV / mm 663.7kV / mm 691.4kV / mm 628.8kV / mm Double cross 638.6kV / mm 687.1kV / mm 695.8kV / mm 636.2kV / mm 3D weaving 653.4kV / mm 699.7kV / mm 737.5kV / mm 687.0kV / mm

[0100] The Weibull distribution of breakdown voltage for a 10% three-dimensional braided composite film is as follows: Figure 3 As shown;

[0101] Table 2

[0102] Energy storage density 5% sample 8% of samples 10% of the samples 15% of samples One direction <![CDATA[15.9J / cm 3 ]]> <![CDATA[21.5J / cm 3 ]]> <![CDATA[19.1J / cm 3 ]]> <![CDATA[17.8J / cm 3 ]]> Double cross <![CDATA[18.3J / cm 3 ]]> <![CDATA[23.8J / cm 3 ]]> <![CDATA[22.5J / cm 3 ]]> <![CDATA[19.9J / cm 3 ]]> 3D weaving <![CDATA[18.5J / cm 3 ]]> <![CDATA[24.9J / cm 3 ]]> <![CDATA[29.3J / cm 3 ]]> <![CDATA[20.9J / cm 3 ]]>

[0103] The discharge energy density of a 10% three-dimensional woven composite film under different electric fields is as follows: Figure 4 As shown;

[0104] Table 3

[0105]

[0106]

[0107] The charge-discharge efficiency of a 10% three-dimensional woven composite film under different electric fields is as follows: Figure 5 As shown;

[0108] Comparison of the highest discharge energy density and breakdown strength of three composite thin films with different structures Figure 6 As shown.

Claims

1. A method for preparing a fiber-woven dielectric membrane for high energy density capacitors, characterized in that: A polyetherimide / polyvinylidene fluoride-hexafluoropropylene composite film with a three-dimensional cross-woven structure was prepared by electrospinning and hot pressing, as follows: Step 1: Weigh a certain mass of polyvinylidene fluoride-hexafluoropropylene powder and place it in a beaker. Add N to the beaker at a volume ratio of 1:

1. - Methylpyrrolidone solvent and acetone were stirred at room temperature to obtain an outer precursor solution; Step 2: Weigh a certain mass of polyetherimide particles and place them in a beaker. Add N to the beaker at a volume ratio of 9:

8. - The inner layer precursor solution was obtained by stirring methylpyrrolidone solvent and acetone at 40 °C. Step 3: Use two 10 mL syringes to draw up the inner and outer layer precursor solutions respectively. Connect the two syringes to the two ports of the specially designed coaxial spinning needle. Apply a high voltage of 16~18 kV to carry out the electrospinning process. The speed of the spinning receiving shaft is 600+50 or 600-50 rpm. The ratio of the propulsion speed of the inner and outer layer solutions is consistent with the ratio of the inner and outer layer areas of the coaxial spinning needle. Step 4: Remove the prepared fiber felt from the aluminum foil and dry it; Step 5: Place three layers of fiber felt in the mold in a cross-vertical direction. First, set the heating table of the hot press to 190 ℃ and preheat for 30 min. After placing the stacked fiber felt in, maintain it at 5 MPa for 10 min, and then depressurize for 5 min to allow the air to be discharged. Then, after pressurizing at 200 °C and 210 °C for 10 min and depressurizing for 5 min respectively, a three-dimensional woven composite film with a polyetherimide volume fraction of 10% was obtained after applying a pressure of 7.5 MPa at 220 °C for 1 h and cooling by blowing air.

2. The method for preparing a fiber-woven dielectric membrane for a high energy density capacitor according to claim 1, characterized in that: In step 3, the product of the ratio of the volume concentration of polyetherimide in the inner precursor solution to the volume concentration of polyvinylidene fluoride-hexafluoropropylene in the outer precursor solution and the ratio of the inner and outer surface areas of the coaxial spinning needle is the volume ratio of polyetherimide to polyvinylidene fluoride-hexafluoropropylene in the resulting spun fiber. 。 3. The method for preparing a fiber-woven dielectric membrane for a high energy density capacitor according to claim 1 or 2, characterized in that: In step 3, the ambient temperature is maintained at 26 ℃ and the humidity is between 10% RH and 30% RH throughout the electrospinning process, and the spinning time is between 12 h and 18 h.

4. The method for preparing a fiber-woven dielectric membrane for a high energy density capacitor according to claim 1, characterized in that: In step 4, excess solvent is removed by drying in air at 120 °C for 2 h, followed by drying in a vacuum for more than 24 h.

5. A fiber-woven dielectric membrane for high energy density capacitors, characterized in that: It is prepared by the method described in any one of claims 1-4.

Images