Multilayer polymer piezoelectric electret material and preparation method thereof

Abstract

The invention discloses a multilayer polymer piezoelectric electret material and a preparation method thereof. The preparation method comprises the following steps: respectively preparing a fiber membrane and a cast membrane through electrostatic spinning and a solution tape casting method; covering the surface of the fiber membrane with a cast film, and alternately overlapping layer by layer to obtain a multi-layer P (VDF-TrFE) electret; carrying out superposition and corona polarization treatment on a plurality of layers of P (VDF-TrFE) electrets; and testing d33 of the piezoelectric electret material after polarization. According to the preparation method, a solution tape casting method, an electrostatic spinning method and corona polarization are creatively combined, the prepared multi-layer P (VDF-TrFE) piezoelectric electret material has good flexibility and mechanical strength, the piezoelectric constant d33 of an electret is tested, the maximum piezoelectric constant test reaches 3314 pC / N, and the product shows high piezoelectric response.

Description

Technical Field

[0001] The present invention belongs to the technical field of electret preparation methods, and specifically relates to a preparation method of a multi-layer polymer piezoelectric electret material, and also relates to a multi-layer polymer piezoelectric electret material. Background Art

[0002] With the rapid development of the Internet of Things, more and more various sensors are applied in fields such as industrial manufacturing, medical and health, security prevention, and wearable devices, playing an important role in environmental monitoring, structural health monitoring, human health monitoring, human-machine interface, motion analysis, etc. Traditional rigid piezoelectric materials are difficult to meet the requirements of flexibility and biocompatibility, which has promoted the exploration of piezoelectric electrets. Therefore, it is of great significance to develop a simple and effective preparation method for flexible piezoelectric electrets. At present, the commonly used preparation methods of traditional single processes all have certain limitations. For example, the single-layer casting film is dense but has high brittleness and is easy to crack. The single-layer electrospun fiber membrane has good flexibility but low mechanical strength and is difficult to bear high loads, and the piezoelectric constant d 33 is relatively low (50 - 200 pC / N). Therefore, a preparation method for piezoelectric electrets with good flexibility, high mechanical strength, and high piezoelectric constant is needed. Summary of the Invention

[0003] The purpose of the present invention is to provide a preparation method for a multi-layer polymer piezoelectric electret material, and solve the problems of poor flexibility and low piezoelectric constant of existing piezoelectric electrets.

[0004] The purpose of the present invention is also to provide a multi-layer polymer piezoelectric electret material.

[0005] The first technical solution adopted by the present invention is: a preparation method for a multi-layer polymer piezoelectric electret material, and the specific operation steps are as follows: Step 1: Dissolve poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) powders with different components and dopamine in N,N-dimethylformamide solvent, and stir evenly to obtain an electrospinning solution; dissolve P(VDF-TrFE) in N,N-dimethylformamide solvent and stir evenly to obtain a casting solution; Step 2: Prepare a fiber membrane by electrospinning method, and prepare a casting membrane by solution casting method; Step 3: Cover the casting membrane obtained by the solution casting method on the surface of the fiber membrane, and obtain a multi-layer P(VDF-TrFE) electret through layer-by-layer alternating stacking; Step 4: After spraying gold on one side of the multi-layer P(VDF-TrFE) electret stack, perform corona polarization treatment to obtain a piezoelectric electret material; Step 5: Test the piezoelectric constant d of the piezoelectric electret material after polarization 33 .

[0006] The features of the present invention also lie in that Further, in the P(VDF-TrFE) powder used in step 1, the molar ratios of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) are 80 / 20, 70 / 30, and 65 / 35 respectively.

[0007] Further, the mass ratio of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) powder in the electrospinning solution in step 1 is 13% - 17%.

[0008] Further, in the multi-layer P(VDF-TrFE) electret in step 3, the outermost layer of the film is a cast film, and the fibrous film is wrapped inside the cast film, and the total number of layers of the cast film and the fibrous film is not less than 3 layers.

[0009] Further, in step 1, the mass of dopamine is 1% of the mass of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) powder; the mass ratio of poly(vinylidene fluoride-trifluoroethylene) P(VDF-TrFE) powder in the casting solution is 8%.

[0010] Further, the electrospinning parameters in step 2 are: the voltage is 18 - 20 kV, the distance from the needle to the collecting roller is 10 - 15 cm, the electrospinning speed is 16.67 μL / min, the ambient temperature is 30 - 40 °C, and the humidity is 20% - 30%.

[0011] Further, the polarization treatment voltage in step 4 is 14 - 16 kV, and the polarization time is 10 min; during the polarization process, the distance between the needle and the surface of the multi-layer P(VDF-TrFE) electret is adjusted to be 1 cm - 5 cm.

[0012] The second technical solution adopted by the present invention is: a multi-layer polymer piezoelectric electret material, which is prepared according to the preparation method of the multi-layer polymer piezoelectric electret material.

[0013] The beneficial effects of the present invention are: 1. Effectively improve the polarization efficiency and charge injection effect The porous structure of the electrospun fibrous film serves as an intermediate layer, allowing the high-voltage electric field during corona polarization to penetrate deeper into the material, promoting the directional arrangement of dipoles in the P(VDF-TrFE) molecular chains, especially enhancing the β-phase transformation efficiency of the intermediate layer and the adjacent cast layers. The high specific surface area and pore structure of the fibrous film can serve as charge trap sites, capturing more injected ions or electrons during the corona polarization process to form a stable space charge layer, improving the surface potential and polarization stability.

[0014] 2. Coordinate and optimize the mechanical and electrical properties The outer cast film provides high density and tensile strength, preventing polarization or mechanical failure of the material during use; the middle fiber layer disperses stress through a porous structure, enhancing the overall flexibility and fatigue resistance. The dielectric constant difference between the cast layer and the fiber layer leads to interfacial polarization, forming an additional polarization electric field at the interface and further strengthening the overall piezoelectric response.

[0015] 3. Enhanced durability and stability The outer dense cast film can reduce charge escape caused by environmental humidity or mechanical deformation, extending the lifespan of the electret; the porous structure of the middle fiber layer evenly disperses the polarization electric field, avoiding the breakdown risk caused by overly strong local electric fields.

[0016] 4. Corona polarization and the multilayer film structure can effectively cooperate Corona polarization does not require high temperatures (traditional thermal polarization requires >100 °C), avoiding interlayer delamination caused by differences in thermal expansion coefficients in the multilayer structure; the non-contact nature of corona polarization avoids mechanical pressure damaging the multilayer structure (such as contact electrode polarization may cause the fiber layer to collapse); by adjusting the corona voltage, electrode distance, and polarization time, the polarization depth and charge distribution can be optimized for different layer structures. Description of the Drawings

[0017] Figure 1 is a scanning electron microscope image of the P(VDF-TrFE) electrospun fiber membrane of the present invention; Figure 2 is a scanning electron microscope image of the P(VDF-TrFE) electrospun fiber membrane of the present invention; Figure 3 is the Q-T curve and d 33 value Figure 4 measured from the single-layer cast film sample prepared in Example 1 of the present invention; 33 value; Figure 5 is the Q-T curve and d 33 value measured from the 3-layer sample prepared in Example 1 of the present invention; Figure 6 is the Q-T curve and d 33 value measured from the sample prepared in Example 2 of the present invention; Figure 7 is the Q-T curve and d 33 value measured from the sample prepared in Example 3 of the present invention; Figure 8 is the Q-T curve and d 33 value measured from the sample prepared in Example 4 of the present invention; Figure 9 is the Q-T curve and d measured from the sample prepared in Example 5 of the present invention;33 Value; Figure 10 The Q-T curve and d measured from the sample prepared in Example 6 of the present invention 33 Value; Figure 11 The Q-T curve and d measured from the sample prepared in Example 7 of the present invention 33 Value. Detailed implementation manners

[0018] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1 Step S1: Preparation of solution; 1.8 g of P(VDF-TrFE) powder with a composition of 70 / 30 was dissolved in 12.6 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain an electrospinning solution with a mass ratio of P(VDF-TrFE) powder of 13%; at the same time, 1.2 g of P(VDF-TrFE) powder was dissolved in 15 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain a solution for subsequent casting.

[0020] Step S2: Preparation of fiber membrane by electrospinning and preparation of casting membrane by solution casting method; The electrospinning solution was transferred into a 10 mL syringe, and the electrospinning parameters were set as follows: voltage 20 kV, distance from the needle to the collecting roller 15 cm, electrospinning speed 16.67 μL / min, ambient temperature 30 °C, humidity 20%, and finally a fiber membrane was obtained on the collecting roller; the prepared solution was dropped onto a glass slide with a dropper, the bubbles were removed and placed in an oven, the solvent was volatilized at 70 °C for 3 h, the polymer was kept in a molten state at 170 °C for 2 h, and finally annealed at 120 °C for 12 h to improve the crystallinity, and finally a casting membrane was obtained.

[0021] Step S3: Stacking of multi-layer P(VDF-TrFE) electrets and corona polarization treatment.

[0022] There was an electrostatic adsorption force remaining on the electrospun fiber membrane. Two casting membranes obtained by the solution casting method were closely attached to both sides of the fiber membrane to obtain a 3-layer electret; the 3-layer sample, the single-layer casting membrane, and the single-layer electrospun fiber membrane were respectively sputter-coated with gold on one side and then placed into a corona polarization device, and polarized at a voltage of 15.4 kV for 10 min. During the polarization process, the distance between the needle and the sample was appropriately adjusted to avoid breakdown.

[0023] Step S4: d 33 Testing.

[0024] Two copper wires were led on the surface of the polarized sample and encapsulated, and the d was measured with the built test system.33 For the test, the test system of the present invention mainly includes three parts: a high-frequency shaker - force control module, an electrometer, and a computer host. The high-frequency shaker can accurately generate excitation forces with different frequencies and amplitudes by connecting with a signal generator and a signal amplifier. Cooperating with the pressure sensor film block group, it can display the magnitude of the excitation force in real time. The change trend of the charge can be immediately viewed through the electrometer. The real-time data curve of charge versus time (Q-t curve) can be observed through the computer host. According to the measured charge quantity by the electrometer and the value of the excitation force, the piezoelectric constant d 33 is calculated using the formula d 33 = Q / F. The test results of the single-layer cast film are as shown in Figure 3 , and d 33 is 150 pC / N. The test results of the single-layer electrospun fiber film are as shown in Figure 4 , and d 33 is 80 pC / N. The test results of the 3-layer sample are as shown in Figure 5 , and d 33 is 1800 pC / N. It can be thus shown that the piezoelectric constant can be significantly increased after the number of piezoelectric electret layers is increased.

[0025] Example 2 Step S1: Preparation of the solution; 1.8 g of P(VDF-TrFE) powder with a composition of 70 / 30 and 0.018 g of dopamine are dissolved in 12.6 mL of N,N-dimethylformamide solvent, and stirred for 12 h to obtain an electrospinning solution with a mass ratio of P(VDF-TrFE) powder of 13%. At the same time, 1.2 g of P(VDF-TrFE) powder is dissolved in 15 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain a solution for subsequent casting.

[0026] Step S2: Preparation of the fiber film by electrospinning and preparation of the cast film by solution casting method; The electrospinning solution is transferred into a 10 mL syringe. The electrospinning parameters are set as follows: voltage is 20 kV, the distance from the needle to the collecting drum is 15 cm, the electrospinning speed is 16.67 μL / min, the ambient temperature is 30 °C, and the humidity is 20%. Finally, a fiber film is obtained on the collecting drum, and the fiber film is characterized by a scanning electron microscope, as shown in Figure 1 ; The prepared solution is dropped onto a glass slide with a dropper, the bubbles are removed and placed in an oven. The solvent is volatilized at 70 °C for 3 hours, the polymer is kept in a molten state at 170 °C for 2 hours, and finally annealed at 120 °C for 12 hours to improve the crystallinity, and finally a cast film is obtained.

[0027] Step S3: Lamination and corona polarization treatment of the multi-layer P(VDF-TrFE) electret.

[0028] There is residual electrostatic adsorption force on the fiber membrane after electrospinning. Two casting films obtained by the solution casting method are closely attached to both sides of the fiber membrane to obtain a three-layer electret; the three-layer sample is sputter-coated with gold on one side and then placed into a corona polarization device. It is polarized for 10 minutes at a voltage of 15.4 kV, and the distance between the needle and the sample is appropriately adjusted during the polarization process to avoid breakdown.

[0029] Step S4: d of the polarized sample 33 Testing.

[0030] Two copper wires are led on the surface of the polarized sample and encapsulated, and the d is tested using the testing system built in Example 1. 33 The test result is as Figure 6 The d 33 is 3314 pC / N, indicating that the addition of dopamine increases the piezoelectric constant.

[0031] Example 3 Step S1: Preparation of the solution; 1.8 g of P(VDF-TrFE) powder with a composition of 80 / 20 and 0.018 g of dopamine are dissolved in 12.6 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain an electrospinning solution with a mass ratio of P(VDF-TrFE) powder of 13%; at the same time, 1.2 g of P(VDF-TrFE) powder is dissolved in 15 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain a solution for subsequent casting.

[0032] Step S2: Preparation of the fiber membrane by electrospinning and the casting film by the solution casting method; The electrospinning solution is transferred into a 10 mL syringe. The electrospinning parameters are set as follows: voltage is 20 kV, the distance from the needle to the collecting roller is 15 cm, the electrospinning speed is 16.67 μL / min, the ambient temperature is 30 °C, and the humidity is 20%. Finally, a fiber membrane is obtained on the collecting roller; the prepared solution is dropped onto a glass slide with a dropper, the bubbles are removed and placed in an oven. The solvent is volatilized at 70 °C for 3 hours, the polymer is kept in a molten state at 170 °C for 2 hours, and finally annealed at 120 °C for 12 hours to improve the crystallinity, and finally a casting film is obtained.

[0033] Step S3: Lamination of multi-layer P(VDF-TrFE) electrets and corona polarization treatment.

[0034] There is residual electrostatic adsorption force on the fiber membrane after electrospinning. Two casting films obtained by the solution casting method are closely attached to both sides of the fiber membrane to obtain a 3-layer electret. On this basis, another layer of electrospun fiber membrane and one layer of cast casting film are attached to obtain a 5-layer electret. The 5-layer sample is sputter-coated with gold on one side and then placed into a corona polarization device, polarized at a voltage of 15.4 kV for 10 min, and the distance between the needle and the sample is appropriately adjusted during the polarization process to avoid breakdown.

[0035] Step S4: d of the polarized sample 33 Testing.

[0036] Two copper wires are led on the surface of the polarized sample and encapsulated, and the d 33 is tested using the testing system built in Example 1. The test results are as Figure 7 , d 33 is 1076 pC / N.

[0037] Example 4 Step S1: Preparation of the solution; 2.9 g of 70 / 30 P(VDF-TrFE) powder and 0.029 g of dopamine are dissolved in 14.25 mL of N,N-dimethylformamide solvent, and stirred for 12 h to obtain an electrospinning solution with a P(VDF-TrFE) powder concentration of 17%. At the same time, 1.2 g of P(VDF-TrFE) powder is dissolved in 15 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain a solution for subsequent casting.

[0038] Step S2: Preparation of the fiber membrane by electrospinning and the casting film by solution casting method; The electrospinning solution is transferred into a 10 mL syringe, and the electrospinning parameters are set as follows: voltage is 18 kV, the distance from the needle to the collecting roller is 12 cm, the electrospinning speed is 0.4 mL / h, the ambient temperature is 30 °C, and the humidity is 30%. Finally, a fiber membrane is obtained on the collecting roller. The prepared solution is dropped onto a glass slide with a dropper, the bubbles are removed and placed in an oven. The solvent is volatilized at 70 °C for 3 h, the polymer is kept in a molten state at 170 °C for 2 h, and finally annealed at 120 °C for 12 h to improve the crystallinity, and finally a casting film is obtained.

[0039] Step S3: Lamination of multi-layer P(VDF-TrFE) electrets and corona polarization treatment There is residual electrostatic adsorption force on the fiber membrane after electrospinning. Two casting films obtained by the solution casting method are closely attached to both sides of the fiber membrane to obtain a 3-layer electret; the 3-layer sample is sputter-coated with gold on one side and then placed into a corona polarization device, polarized at a voltage of 15.4 kV for 10 min, and the distance between the needle and the sample is appropriately adjusted during the polarization process to avoid breakdown.

[0040] Step S4: Measurement of d of the polarized sample 33 Measurement.

[0041] Two copper wires are led on the surface of the polarized sample and encapsulated, and the device is used to measure d 33 The measurement result is as Figure 8 , d 33 is 1882 pC / N.

[0042] Example 5 Step S1: Preparation of the solution; 2.9 g of 80 / 20P(VDF-TrFE) powder and 0.029 g of dopamine are dissolved in 14.25 mL of N,N-dimethylformamide solvent, and stirred for 12 h to obtain an electrospinning solution with a P(VDF-TrFE) powder concentration of 17%; at the same time, 1.2 g of P(VDF-TrFE) powder is dissolved in 15 mL of N,N-dimethylformamide solvent and stirred for 12 h to obtain a solution for subsequent casting.

[0043] Step S2: Preparation of the fibrous membrane by electrospinning and the casting membrane by the solution casting method; The electrospinning solution is transferred into a 10 mL syringe, and the electrospinning parameters are set as follows: the voltage is 18 kV, the distance from the needle to the collecting roller is 12 cm, the electrospinning speed is 0.4 mL / h, the ambient temperature is 30 °C, and the humidity is 30%. Finally, a fibrous membrane is obtained on the collecting roller; the prepared solution is dropped onto a glass slide with a dropper, the bubbles are removed and placed in an oven, the solvent is volatilized at 70 °C for 3 h, the polymer is kept in a molten state at 170 °C for 2 h, and finally annealed at 120 °C for 12 h to improve the crystallinity, and finally a casting membrane is obtained.

[0044] Step S3: Lamination and corona polarization treatment of multi-layer P(VDF-TrFE) electrets There is an electrostatic adsorption force remaining on the fibrous membrane after electrospinning. Two casting membranes obtained by the solution casting method are closely attached to both sides of the fibrous membrane to obtain a 3-layer electret. On this basis, 1 layer of electrospun fibrous membrane and 1 layer of cast casting membrane are attached to obtain a 5-layer electret; the 5-layer sample is sputtered with gold on one side and then placed in a corona polarization device, and polarized at a voltage of 15.4 kV for 10 min. During the polarization process, the distance between the needle and the sample is appropriately adjusted to avoid breakdown.

[0045] Step S4: Measurement of d of the polarized sample 33 Measurement.

[0046] Two copper wires are led on the surface of the polarized sample and encapsulated, and the device is used to measure d 33 The measurement result is as Figure 9 , d 33 is 1112 pC / N.

[0047] Example 6 Step S1: Preparation of the solution.

[0048] Dissolve 1.8 g of P(VDF-TrFE) powder with a composition of 65 / 35 and 0.018 g of dopamine in 12.6 mL of N,N-dimethylformamide solvent, and stir for 12 h to obtain an electrospinning solution with a mass ratio of P(VDF-TrFE) powder of 13%; at the same time, dissolve 1.2 g of P(VDF-TrFE) powder in 15 mL of N,N-dimethylformamide solvent and stir for 12 h to obtain a solution for subsequent casting.

[0049] Step S2: Prepare a fiber membrane by electrospinning and a cast film by solution casting method; Transfer the electrospinning solution into a 10 mL syringe, and set the electrospinning parameters as follows: voltage is 18 kV, the distance from the needle to the collecting roller is 12 cm, the electrospinning speed is 0.4 mL / h, the ambient temperature is 30 °C, and the humidity is 30%. Finally, a fiber membrane is obtained on the collecting roller; use a dropper to drop the prepared solution onto a glass slide, remove the bubbles and place it in an oven. Volatilize the solvent at 70 °C for 3 hours, keep the polymer in a molten state at 170 °C for 2 hours, and finally anneal at 120 °C for 12 hours to improve the crystallinity, and finally obtain a cast film.

[0050] Step S3: Stacking and corona polarization treatment of multi-layer P(VDF-TrFE) electrets There is an electrostatic adsorption force remaining on the electrospun fiber membrane. Stick two cast films obtained by the solution casting method on both sides of the fiber membrane to obtain a 3-layer electret; spray gold on one side of the 3-layer electret and place it in a corona polarization device. Polarize it at a voltage of 15.4 kV for 10 min, and appropriately adjust the distance between the needle and the sample during the polarization process to avoid breakdown.

[0051] Step S4: d of the polarized sample 33 Testing.

[0052] Lead two copper wires on the surface of the polarized sample and encapsulate it, and use the equipment to perform d 33 testing, and the test results are as Figure 10 shown, d 33 is 1645 pC / N.

[0053] Example 7 Step S1: Preparation of the solution; Dissolve 2.9 g of the component 65 / 35 P(VDF-TrFE) powder and 0.029 g of dopamine in 14.25 mL of N,N-dimethylformamide solvent, and stir for 12 h to obtain an electrospinning solution with a P(VDF-TrFE) powder concentration of 17%; at the same time, dissolve 1.2 g of P(VDF-TrFE) powder in 15 mL of N,N-dimethylformamide solvent and stir for 12 h to obtain a solution for subsequent casting.

[0054] Step S2: Prepare a fiber membrane by electrospinning and a cast film by solution casting; Transfer the electrospinning solution into a 10 mL syringe, and set the electrospinning parameters as follows: voltage is 18 kV, the distance from the needle to the collecting roller is 12 cm, the electrospinning speed is 0.4 mL / h, the ambient temperature is 30 °C, and the humidity is 30%. Finally, obtain a fiber membrane on the collecting roller; use a dropper to drop the prepared solution onto a glass slide, remove the bubbles and place it in an oven. Volatilize the solvent at 70 °C for 3 hours, keep the polymer in a molten state at 170 °C for 2 hours, and finally anneal at 120 °C for 12 hours to improve the crystallinity, and finally obtain a cast film.

[0055] Step S3: Superposition and corona polarization treatment of multi-layer P(VDF-TrFE) electrets There is an electrostatic adsorption force remaining on the fiber membrane after electrospinning. Press two cast films obtained by solution casting tightly on both sides of the fiber membrane to obtain a 3-layer electret. On this basis, attach 1 layer of electrospun fiber membrane and 1 layer of cast film to obtain a 5-layer electret; spray gold on one side of the 5-layer sample and place it in a corona polarization device, and polarize it at a voltage of 15.4 kV for 10 min. During the polarization process, appropriately adjust the distance between the needle and the sample to avoid breakdown.

[0056] Step S4: d of the polarized sample 33 Testing.

[0057] Lead two copper wires on the surface of the polarized sample and encapsulate it, and use the equipment to perform d 33 testing, and the test results are as Figure 11 shown, and d 33 is 1063 pC / N.

[0058] The present invention includes steps such as the preparation of solutions, the preparation of electrospun fiber membranes and solution-cast films, the superposition and corona polarization treatment of multi-layer electrets, encapsulation, and d 33 testing of electrets. The prepared multi-layer piezoelectric electret material can not only integrate the advantages of single-layer electret materials, have better flexibility and mechanical strength, but also show higher piezoelectric response.

[0059] Figure 1It is the scanning electron microscope image of the electrospun fiber membrane of P(VDF-TrFE) of the present invention. The magnification is 1000 times. The fiber network is complete and there are no obvious defects; Figure 2 The magnification of is 4000 times, and the fiber diameters are relatively consistent.

[0060] In summary, the electret of P(VDF-TrFE) prepared by the present invention is obtained by polarizing the fiber membrane and the cast film prepared based on electrospinning and solution casting methods after multi-layer stacking. The electret has the characteristics of good flexibility, high mechanical strength, and good piezoelectric response effect; the technical effect is the best when the molar ratio of polyvinylidene fluoride to trifluoroethylene in the P(VDF-TrFE) powder is 70 / 30.

[0061] The above are only some embodiments of the present invention. For those skilled in the art, without departing from the principle of the present invention, several improvements and refinements made to the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a multilayer polymer piezoelectric electret material, characterized in that: The specific steps are as follows: Step 1: Dissolve polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) powders of different components and dopamine in N,N-dimethylformamide solvent, stir evenly to obtain electrospinning solution; dissolve P (VDF-TrFE) in N,N-dimethylformamide solvent and stir evenly to obtain casting solution; Step 2: preparing a fiber membrane by electrospinning, and preparing a cast membrane by solution casting; Step 3: Covering the cast film obtained by the solution casting method on the surface of the fiber membrane, and alternately stacking layer by layer to obtain a multilayer P (VDF-TrFE) electret; Step 4: After the multi-layer P (VDF-TrFE) electret is superimposed and gold is sprayed on one side, a corona poling treatment is performed to obtain a piezoelectric electret material; Step 5: Test the piezoelectric constant d of the piezoelectric electret material after polarization 33 .

2. The method for preparing a multilayer polymer piezoelectric electret material according to claim 1, characterized in that: The molar ratios of vinylidene fluoride VDF and trifluoroethylene TrFE in the P (VDF-TrFE) powder used in step 1 are 80 / 20, 70 / 30, and 65 / 35, respectively.

3. The method for preparing the multilayer polymer piezoelectric electret material according to claim 1, characterized in that: The mass proportion of polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) powder in the electrospinning solution in step 1 is 13%-17%.

4. The method for preparing a multilayer polymer piezoelectric electret material according to claim 1, characterized in that: In step 3, the outermost film in the multilayer P (VDF-TrFE) electret is a cast film, and the fiber film is wrapped in the cast film. The total number of layers of the cast film and the fiber film is not less than 3 layers.

5. The method for preparing a multilayer polymer piezoelectric electret material according to claim 1, characterized in that: The mass of the dopamine in step 1 is 1% of the mass of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) powder; the mass proportion of the polyvinylidene fluoride-trifluoroethylene P (VDF-TrFE) powder in the casting solution is 8%.

6. The method for preparing a multilayer polymer piezoelectric electret material according to claim 1, characterized in that: The electrospinning parameters in step 2 are: voltage of 18-20 kV, distance from needle to collecting drum of 10-15 cm, electrospinning speed of 16.67 μL / min, ambient temperature of 30-40° C., and humidity of 20%-30%.

7. The method for preparing a multilayer polymer piezoelectric electret material according to claim 2, characterized in that: The polarization treatment voltage in step 4 is 14-16 kV, and the polarization time is 10 min.

8. The method for preparing a multilayer polymer piezoelectric electret material according to claim 7, characterized in that: During the poling process, the distance between the needle and the multilayer P (VDF-TrFE) electret surface was adjusted to 1 cm-5 cm.

9. A multilayer polymer piezoelectric electret material, characterized in that: It is prepared according to the preparation method of the multilayer polymer piezoelectric electret material according to any one of claims 1 to 8.

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