A branch-stem heterogeneous structure piezoelectric fiber, piezoelectric nanogenerator, and preparation method and application thereof

Abstract

This invention belongs to the field of electronic device technology and discloses a branch-heterogeneous piezoelectric fiber, a piezoelectric nanogenerator, and its preparation method and application, to address the low effective polarization voltage of the piezoelectric filler in flexible piezoelectric nanogenerators. The invention combines chemical gelation and coaxial electrospinning technology to "graft" barium titanate-based nanospheres coated with nano-Ag (BCZT-SP@Ag) onto the surface of a barium titanate-based fiber, creating a branch-heterogeneous piezoelectric fiber (BCZT-NF@BCZT-SP@Ag). The BCZT-SP@Ag fiber with a heterogeneous structure on the fiber surface can regulate the interface region to enhance carrier activity near the piezoelectric filler, thereby improving the effective polarization electric field and enhancing the output performance of a PENG. Using polyvinylidene fluoride as a flexible matrix, a PENG based on a BCZT-NF@BCZT-SP@Ag / PVDF composite film is prepared, which can provide high piezoelectric output. The PENG prepared using this technology can be applied to power grids to construct a PENG-based wire vibration sensing and monitoring system.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic devices, and in particular to a branch-stem heterogeneous structure piezoelectric fiber, a piezoelectric nanogenerator, and a preparation method and application thereof. Background Art

[0002] Flexible piezoelectric nanogenerators (PENGs) based on organic / inorganic composite films can harvest electrical energy from their surroundings. They are widely used in the Internet of Things (IoT) to capture clean energy to power low-power electronic devices, alleviating energy crises and reducing maintenance costs associated with battery replacement. PENGs can also serve as active sensing units to capture electrical signals from the environment, making them ideal for self-powered monitoring and sensing systems. Conventionally, such flexible PENGs are prepared by incorporating inorganic piezoelectric fillers into an organic polymer matrix at appropriate proportions to form a composite film. The composite film is then polarized and encapsulated into a PENG. The inorganic piezoelectric fillers provide the PENG with excellent piezoelectric properties, directly affecting its electrical output. The organic polymer material, on the other hand, offers excellent flexibility, enabling the PENG to meet the demands of diverse operating conditions. However, conventional PENG fabrication techniques encapsulate the piezoelectric filler within a highly insulating polymer matrix. This results in the polymer dissipating the majority of the polarization voltage during the composite material's polarization process, resulting in a low effective polarization voltage acting on the piezoelectric filler. This significantly impacts the PENG's output and limits its applications in sensing and monitoring. For example, our group previously filed a patent application, publication number CN117161378A, entitled "A Piezoelectric Nanogenerator, Preparation Method, and Wireless Sensing System." This approach involves coaxially electrospinning a solution (a) containing barium titanate / PVDF with silver nanospheres enriched on its surface, and a solution (b) containing barium titanate / PVDF, with solution (a) forming the inner and outer sides of the coaxial fibers. This synthesis method allows for the preparation of high-performance PENGs through a single electrospinning process, offering advantages such as a simple synthesis process and excellent performance. However, this process lacks microstructural design of the piezoelectric filler to optimize the effective polarization field. Therefore, it is of great significance to further optimize the design of the piezoelectric fiber microstructure to further improve the electrical output of PENG. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention proposes a branch-stem heterostructure piezoelectric fiber, a piezoelectric nanogenerator, and a preparation method and application thereof.

[0004] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0005] A method for preparing a branch-stem heterogeneous structure piezoelectric fiber, comprising the following steps:

[0006] (1) BaCl2·H2O, CaCl2, ZrOCl2·8H2O, and tetrabutyl titanate were dissolved in water, and NaOH was added to obtain a mixed solution. Barium titanate-based nanospheres (BCZT-SP) were prepared by a hydrothermal method. The obtained BCZT-SP was dissolved in a solvent to obtain solution 2.

[0007] (2) Ba(OH)2·8H2O, Ca(OH)2, Zr(C5H7O2)4 and tetrabutyl titanate were dissolved in a mixed solvent of acetic acid and ethylene glycol methyl ether to obtain solution 1;

[0008] (3) Solution 1 and solution 2 were coaxially electrospun and then sintered to prepare BCZT-NF@BCZT-SP piezoelectric fibers; solution 1 was the coaxial electrospun inner layer structure solution, and solution 2 was the coaxial electrospun outer layer structure solution;

[0009] (4) Ag nanoparticles were deposited on the BCZT-NF@BCZT-SP piezoelectric fibers prepared in step (3) using a chemical reduction method to prepare branch-stem heterostructure piezoelectric fibers.

[0010] In the above step (1), the molar ratio of BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate is (8-9):(1.2-1.6):(0.8-1.1):(9.5-10.5), and the Ba in the mixed solution is 2+ The concentration is 0.07-0.09 mol / L, Ba 2+ With OH - The molar ratio of the hydrothermal method is 1:(4-6); the reaction temperature of the hydrothermal method is 190-210°C and the reaction time is 18-24 h.

[0011] In the solution 2 of the above step (1), the solvent is a mixed solvent of acetic acid, ethylene glycol methyl ether and acetylacetone (the volume ratio of the three is 6:6:1), and the molar concentration of BCZT-SP is 0.04-0.07 mol / L.

[0012] Furthermore, polyvinyl pyrrolidone is added to the solution 2 in the above step (1) to adjust the viscosity of the solution.

[0013] In the above step (2), the molar ratio of Ba(OH)2·8H2O, Ca(OH)2, Zr(C5H7O2)4 and tetrabutyl titanate is (8-9):(1-2): (0.6-1.2): (9-10). 2+ The concentration is 0.33-0.38 mol / L.

[0014] The process parameters of the coaxial electrospinning technology in the above step (3) are: voltage 16-18 kV, roller speed 200-300 rpm, injection flow rate 15-20 μL / min; sintering temperature is 750-800℃, and time is 4-6 h.

[0015] The specific steps of the chemical reduction method in step (4) above are:

[0016] (S1) BCZT-NF@BCZT-SP piezoelectric fibers were added to a mixed solution of SnCl2 and HCl (I). After stirring for 1-2 hours, the resulting particles were filtered and washed, and then placed in a silver ammonia solution and stirred for 0.5-1.5 hours to obtain BCZT-NF@BCZT-SP with Ag crystals on the surface.

[0017] (S2) placing the BCZT-NF@BCZT-SP with Ag crystallite coated on its surface in step (S1) in a mixed solution II consisting of formaldehyde solution, silver ammonia solution and alcohol, stirring and reacting to obtain a branch-stem heterostructure piezoelectric fiber.

[0018] In the mixed solution I in the above step (S1), the concentration of SnCl2 is 0.06-0.08 mol / L, the concentration of HCl is 0.01-0.02 mol / L, and the concentration of silver ammonia solution is 0.25-0.45 mol / L.

[0019] The volume ratio of formaldehyde solution, silver ammonia solution and alcohol in the mixed solution II in the above step (S2) is (1-1.5): (4-8): (8-12), and the mass volume ratio of BCZT-NF@BCZT-SP coated with Ag crystallites to the mixed solution II is 1 g: (35-45) mL.

[0020] Furthermore, in the above step (S2), the concentration of the formaldehyde solution is 0.02-0.04 mol / L, the concentration of the silver ammonia solution is 0.25-0.45 mol / L, and the alcohol concentration is above 99.5%.

[0021] Furthermore, the stirring reaction time in the above step (S2) is at least 24 hours to facilitate sufficient reaction.

[0022] The branch-stem heterogeneous structure piezoelectric fiber is prepared using the above preparation method.

[0023] The above-mentioned branch-stem heterostructure piezoelectric fiber is used as a filler in a piezoelectric nanogenerator.

[0024] A method for preparing a piezoelectric nanogenerator based on a branch-stem heterostructure piezoelectric fiber comprises the following steps:

[0025] (a) adding branch-stem heterostructure piezoelectric fibers and polyvinylidene fluoride to N,N-dimethylacetamide and stirring, and preparing the resulting mixture into a composite film on a coating machine by a casting method;

[0026] (b) The composite film prepared in step (a) is encapsulated into a piezoelectric nanogenerator via electrodes and polyimide.

[0027] Furthermore, in step (a), the mass ratio of the branch-stem heterostructure piezoelectric fiber to polyvinylidene fluoride is 1:4; and the concentration of the heterostructure piezoelectric fiber in the mixed solution is 0.02-0.04 g / mL.

[0028] Furthermore, the stirring time in step (a) is 8-10 hours.

[0029] The piezoelectric nanogenerator (PENG) was obtained using the above preparation method.

[0030] The piezoelectric nanogenerator is applied to a monitoring sensor system of a power grid anti-vibration device.

[0031] Furthermore, the monitoring and sensing system for power grid vibration isolation devices constructed based on the PENG of the present invention uses the PENG as an active sensor to capture the vibration signal of the conductor and transmit it to a computer receiving end for identification and judgment. The system can then judge the vibration isolation device based on the vibration status of the transmission line.

[0032] The beneficial effects produced by the present invention are:

[0033] (1) The present invention provides a solution to the problem of low effective polarization electric field in flexible materials based on organic / inorganic composite membranes, thereby improving the output performance of PENG. The present invention designs a branch-heterogeneous structure piezoelectric fiber filler. Combining the chemical sol-gel method and coaxial electrospinning technology, barium titanate-based nanospheres (BCZT-SP@Ag) coated with nano-Ag are "grafted" onto the surface of barium titanate-based fibers (BCZT-NF) to form a branch-heterogeneous structure piezoelectric fiber (BCZT-NF@BCZT-SP@Ag). In the present invention, the carrier activity in the organic / inorganic material interface region can be optimized by adjusting the structural ratio of the piezoelectric filler (BCZT-NF@BCZT-SP@Ag), thereby improving the effective polarization electric field and further improving the output performance of PENG. Subsequently, a PENG based on the BCZT-NF@BCZT-SP@Ag / PVDF composite film was prepared using polyvinylidene fluoride (PVDF) as a flexible matrix. The PENG prepared using the technology of the present invention can provide a high piezoelectric output (the maximum output voltage can be as high as 96.4V) and an output current of 15.52µA. The enhanced output performance is more conducive to the practical application of PENG in the field of sensing and monitoring.

[0034] (2) The PENG prepared by the present invention is applied to the power grid to construct a PENG-based wire vibration sensing and monitoring system. In the power grid vibration isolation device monitoring and sensing system constructed by the PENG of the present invention, the PENG acts as an active sensor to capture the vibration signal of the wire and transmit it to the computer receiving end for identification and judgment. The system can judge the vibration isolation device based on the vibration state of the transmission line. Then, the three results are learned and judged through machine learning. The specific process of machine learning is: a deep learning model is used to classify the one-dimensional time series signal. Moreover, as the training process progresses, the classification performance of the model gradually improves and tends to be stable. Finally, the judgment accuracy of the system based on the PENG of the present invention can reach more than 95%.

[0035] (3) The present invention effectively improves the electrical output performance of PENG by designing the microstructure of piezoelectric fibers, thereby expanding the application scenarios of PENG. By combining the PENG in the present invention with machine learning, a system for abnormal monitoring of anti-vibration devices of power transmission lines is designed, which is conducive to the realization of self-powered smart grid sensors and reduces on-site maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0037] Figure 1 This is the preparation process of the nanogenerator based on the branch-stem heterostructure piezoelectric fiber of the present invention.

[0038] Figure 2 SEM image (a) of the branch-stem heterogeneous structure fiber; XRD pattern (b); TEM image (c) and SEM image (d) of the composite film cross section.

[0039] Figure 3 (a) Polarization potential simulation, (b) generated piezoelectric potential simulation, and (c) electrical output test of PENG based on three different piezoelectric fiber fillers.

[0040] Figure 4 Figure 3. Display images of the monitoring sensor system for a power grid vibration isolation device built based on the PENG of the present invention in normal operation (a) and abnormal state (b). (c-e) Feature data extraction based on PENG monitoring in three states. (f) Training accuracy. (h) Training error. (i) Checkerboard diagram for training result determination. DETAILED DESCRIPTION

[0041] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] Raw materials: BaCl2·H2O (99.5%), ZrOCl2·8H2O (98%), CaCl2 (96%), and tetrabutyl titanate were purchased from Aladdin Chemical Reagent Co., Ltd.; polyvinylidene fluoride (average molecular weight Mw ~275,000), Ba(OH)2·8H2O (98%), Ca(OH)2 (99%), and Zr(C5H7O2)4 (97%) were purchased from Sigma-Aldrich Chemical Reagent Co., Ltd. AgNO3 (99%) and SnCl2 (98%) were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0043] Example 1

[0044] A preparation method of a branch-stem heterogeneous structure piezoelectric fiber of this embodiment is shown in the preparation flow chart. Figure 1 As shown, the steps are as follows:

[0045] (1) BCZT-SP was prepared by hydrothermal method using BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate as raw materials. 1.91 g of BaCl2·H2O, 0.16 g of CaCl2, 0.31 g of ZrOCl2·8H2O and 3.23 g of tetrabutyl titanate were uniformly stirred in 100 mL of distilled water and placed in a reactor. An appropriate amount of NaOH was added to the reactor to make BaCl2·H2O and CaCl2·ZrOCl2·8H2O uniformly stirred in 100 mL of distilled water and placed in a reactor. 2+ With OH - The ratio of BCZT to SP is 1:5. The mixed solution in the reactor is reacted at 200℃ for 24 hours, and the obtained material is the synthesized BCZT-SP.

[0046] (2) Ba(OH)2·8H2O, Zr(C5H7O2)4, Ca(OH)2 and tetrabutyl titanate were used as raw materials for preparing BCZT-NF. BCZT-NF@BCZT-SP piezoelectric fibers were prepared by coaxial electrospinning technology. 2.7 g of Ba(OH)2·8H2O, 0.11 g of Ca(OH)2, 0.49 g of Zr(C5H7O2)4 and 3.06 g of tetrabutyl titanate were mixed with 12 mL of acetic acid and 12 mL of ethylene glycol methyl ether to prepare solution 1. 0.4 g of BCZT-SP (0.0018 mol) was mixed with 26 mL of solvent (a mixture of acetic acid, ethylene glycol methyl ether and acetylacetone in a volume ratio of 6:6:1) to prepare solution 2. The viscosity of the solution was adjusted by adding 3 g of polyvinyl pyrrolidone. The sol was prepared into low-humidity prefabricated fibers using coaxial electrospinning technology at a voltage of 18 kV, a spindle speed of 200 rpm, and an injection flow rate of 20 μL / min ( Figure 1 a). The low-humidity prefabricated fiber is placed in a muffle furnace and sintered to obtain BCZT-NF@BCZT-SP piezoelectric fiber ( Figure 1 b), sintering temperature is 750℃ and time is 4.5 h.

[0047] (3) Ag nanoparticles were deposited on high surface energy BCZT-SP by chemical reduction to prepare branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). First, 0.3 g of BCZT-NF@BCZT-SP fibers were washed with deionized water and added to a mixed solution of 1.5 mL of SnCl2 and 1 mL of HCl, where the concentration of SnCl2 was 0.07 mol / L and the concentration of HCl was 0.01 mol / L, and stirred for 2 h. Then, the obtained particles were filtered and washed with deionized water and placed in 40 mL of silver ammonia solution with a concentration of 0.3 mol / L and stirred for 1 h to allow Ag nanocrystals to be coated on the surface of BCZT-NF@BCZT-SP. Finally, 0.3 g of BCZT-NF@BCZT-SP fibers with Ag crystals on the surface were placed in a mixed solution consisting of 1 mL of formaldehyde solution, 4 mL of silver ammonia solution and 8 mL of alcohol and stirred for at least 24 h for sufficient reaction to obtain branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag)( Figure 1 c), wherein the concentration of the formaldehyde solution is 0.02 mol / L, the concentration of the silver ammonia solution is 0.3 mol / L, and the concentration of the alcohol is above 99.5%.

[0048] Figure 2a is a scanning electron microscope (SEM) microscopic image of the branch-stem heterostructured BCZT-NF@BCZT-SP@Ag fiber. The fiber diameter is 200-400 nm, and the heterostructured BCZT-SP@Ag particles have been successfully "grafted" onto the BCZT fiber. Figure 2 b is the X-ray diffraction test pattern (XRD) of the branch-stem heterostructure fiber, in which the diffraction peaks at approximately 21.9°, 31.7°, 38.1°, 45.2°, 55.7° and 65.4° correspond to the (100), (110), (111), (200), (211) and (220) crystal planes of BCZT, respectively; and the diffraction peaks at 38.5°, 44.2°, 64.2° and 77.5° correspond to the (111), (200), (220) and (311) crystal planes of face-centered cubic structure Ag, respectively. Figure 2 c is a TEM photo of a single branch-structured fiber with a diameter of about 200 nm. From the local magnified image, it can be seen that Ag nanoparticles are attached to the surface of BCZT-SP, forming a heterogeneous structure.

[0049] A method for preparing a nanogenerator based on branch-stem heterostructure piezoelectric fibers, the preparation flow chart of which is as follows: Figure 1 As shown, the steps are as follows:

[0050] 0.75 g of BCZT-NF@BCZT-SP@Ag prepared in this example and 3 g of polyvinylidene fluoride were stirred in 30 mL of N,N-dimethylacetamide for 8 h ( Figure 1 d). The obtained mixed solution is prepared into a composite film on a coating machine by a casting method ( Figure 1 e), and then encapsulated by electrodes and polyimide to form PENG ( Figure 1 f).

[0051] Figure 2 d is the cross-sectional SEM image of the composite membrane made by incorporating BCZT-NF@BCZT-SP@Ag fibers into the PVDF matrix. It can be seen from the figure that the BCZT-NF@BCZT-SP@Ag fibers (in the red circle) are relatively evenly distributed in the PVDF, and no obvious agglomeration is formed.

[0052] Figure 3Figures 3a and 3b are simulations of the polarization potential and piezoelectric potential of three PENGs based on different piezoelectric fibers (traditional BCZT-NF fibers, improved BCZT-NF@BCZT-SP fibers, and branch-heterogeneous structured BCZT-NF@BCZT-SP@Ag fibers) under the same polarization conditions using COMOSL multi-physics simulation software. The results show that the present invention can significantly improve the polarization voltage distribution acting on the fiber filler, increase the polarization potential difference, and fully polarize the piezoelectric filler, from 2.6 kV to 7.2 kV ( Figure 3 a); then, under the action of 30 N external force, Figure 3 b shows the piezoelectric potential generated by the PENG on the surface. The results show that the designed branch-stem heterostructure fiber can generate a larger piezoelectric potential, which increases from 22 V to 48 V. Figure 3 Figure c is the electrical output test of PENG based on the three piezoelectric fibers mentioned above. The results show that compared with traditional fiber fillers, the fiber fillers designed based on the present invention can improve the output performance of PENG by more than 3 times, with the output voltage increased from 30.6 V to 96.4 V, and the output current increased from 2.40 μA to 15.52 μA. The enhanced output performance is more conducive to the practical application of PENG in the field of sensing and monitoring.

[0053] Example 2

[0054] A preparation method of a branch-stem heterogeneous structure piezoelectric fiber of this embodiment is shown in the preparation flow chart. Figure 1 As shown, the steps are as follows:

[0055] (1) BCZT-SP was prepared by hydrothermal method using BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate as raw materials. 2.04 g of BaCl2·H2O, 0.13 g of CaCl2, 0.26 g of ZrOCl2·8H2O and 3.57 g of tetrabutyl titanate were uniformly stirred in 100 mL of distilled water and placed in a reactor. An appropriate amount of NaOH was added to the reactor to make BaCl2·H2O and CaCl2·ZrOCl2·8H2O uniformly stirred in 100 mL of distilled water and placed in a reactor. 2+ With OH - The ratio of BCZT to SP is 1:4. The mixed solution in the reactor is reacted at 210℃ for 18 h, and the obtained material is the synthesized BCZT-SP.

[0056] (2) Ba(OH)2·8H2O, Zr(C5H7O2)4, Ca(OH)2 and tetrabutyl titanate were used as raw materials for preparing BCZT-NF. BCZT-NF@BCZT-SP piezoelectric fibers were prepared by coaxial electrospinning technology. 2.52 g of Ba(OH)2·8H2O, 0.074 g of Ca(OH)2, 0.478 g of Zr(C5H7O2)4 and 3.06 g of tetrabutyl titanate were mixed with 12 mL of acetic acid and 12 mL of ethylene glycol methyl ether to prepare solution 1. 0.22 g of BCZT-SP (0.001 mol) was mixed with 26 mL of solvent (a mixture of acetic acid, ethylene glycol methyl ether and acetylacetone in a volume ratio of 6:6:1) to prepare solution 2. The viscosity of the solution was adjusted by adding 3 g of polyvinyl pyrrolidone. The sol was prepared into low-moisture preformed fibers using coaxial electrospinning at a voltage of 16 kV, a spindle speed of 300 rpm, and an injection flow rate of 15 μL / min. The low-moisture preformed fibers were sintered in a muffle furnace at 800°C for 4 hours to obtain BCZT-NF@BCZT-SP piezoelectric fibers.

[0057] (3) Ag nanoparticles were deposited on high surface energy BCZT-SP by chemical reduction to prepare branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). First, 0.3 g of BCZT-NF@BCZT-SP fibers were washed with deionized water and added to a mixed solution of 1.5 mL of SnCl2 and 1 mL of HCl, where the concentration of SnCl2 was 0.06 mol / L and the concentration of HCl was 0.02 mol / L, and stirred for 2 hours. Subsequently, the obtained particles were filtered and washed with deionized water and placed in 40 mL of a 0.25 mol / L silver ammonia solution and stirred for 1 hour to allow the Ag nanocrystals to coat the surface of the BCZT-NF@BCZT-SP. Finally, 0.38 g of BCZT-NF@BCZT-SP fibers covered with Ag crystals were placed in a mixed solution consisting of 1 mL of formaldehyde solution, 4 mL of silver ammonia solution, and 12 mL of alcohol and stirred for at least 24 hours for sufficient reaction to obtain branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). The concentration of the formaldehyde solution was 0.03 mol / L, the concentration of the silver ammonia solution was 0.25 mol / L, and the concentration of the alcohol was above 99.5%.

[0058] A method for preparing a nanogenerator based on branch-stem heterostructure piezoelectric fibers, the preparation flow chart of which is as follows: Figure 1 As shown, the steps are as follows:

[0059] 0.6 g of BCZT-NF@BCZT-SP@Ag prepared in this example was thoroughly stirred with 2.4 g of polyvinylidene fluoride in 30 mL of N,N-dimethylacetamide for 10 hours. The resulting mixture was cast into a composite membrane on a coating machine, which was then encapsulated with electrodes and polyimide to form a PENG.

[0060] Example 3

[0061] A preparation method of a branch-stem heterogeneous structure piezoelectric fiber of this embodiment is shown in the preparation flow chart. Figure 1 As shown, the steps are as follows:

[0062] (1) BCZT-SP was prepared by hydrothermal method using BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate as raw materials. 1.81 g of BaCl2·H2O, 0.18 g of CaCl2, 0.35 g of ZrOCl2·8H2O and 3.40 g of tetrabutyl titanate were uniformly stirred in 114 mL of distilled water and placed in a reactor. An appropriate amount of NaOH was added to the reactor to make BaCl2·H2O and CaCl2·ZrOCl2·8H2O uniformly stirred in 114 mL of distilled water and placed in a reactor. 2+ With OH - The ratio of BCZT to SP is 1:6. The mixed solution in the reactor is reacted at 190 °C for 24 h, and the obtained material is the synthesized BCZT-SP.

[0063] (2) Ba(OH)2·8H2O, Zr(C5H7O2)4, Ca(OH)2 and tetrabutyl titanate were used as raw materials for preparing BCZT-NF. BCZT-NF@BCZT-SP piezoelectric fibers were prepared by coaxial electrospinning technology. 2.84 g of Ba(OH)2·8H2O, 0.15 g of Ca(OH)2, 0.29 g of Zr(C5H7O2)4 and 3.40 g of tetrabutyl titanate were mixed with 12 mL of acetic acid and 12 mL of ethylene glycol methyl ether to prepare solution 1. 0.3 g of BCZT-SP (0.0013 mol) was mixed with 26 mL of solvent (a mixture of acetic acid, ethylene glycol methyl ether and acetylacetone in a volume ratio of 6:6:1) to prepare solution 2. The viscosity of the solution was adjusted by adding 3 g of polyvinyl pyrrolidone. The sol was prepared into low-moisture preformed fibers using coaxial electrospinning at a voltage of 17 kV, a spindle speed of 250 rpm, and an injection flow rate of 17 μL / min. The low-moisture preformed fibers were sintered in a muffle furnace at 750°C for 6 h to obtain BCZT-NF@BCZT-SP piezoelectric fibers.

[0064] (3) Ag nanoparticles were deposited on high surface energy BCZT-SP by chemical reduction to prepare branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). First, 0.3 g of BCZT-NF@BCZT-SP fibers were washed with deionized water and added to a mixed solution of 1.5 mL of SnCl2 and 1 mL of HCl, where the concentration of SnCl2 was 0.08 mol / L and the concentration of HCl was 0.015 mol / L, and stirred for 2 hours. Subsequently, the obtained particles were filtered and washed with deionized water and placed in 40 mL of a 0.45 mol / L silver ammonia solution and stirred for 1 hour to allow the Ag nanocrystals to coat the surface of the BCZT-NF@BCZT-SP. Finally, 0.48 g of BCZT-NF@BCZT-SP fibers covered with Ag crystals were placed in a mixed solution consisting of 1 mL of formaldehyde solution, 8 mL of silver ammonia solution, and 8 mL of alcohol and stirred for at least 24 hours for sufficient reaction to obtain branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). The concentration of the formaldehyde solution was 0.04 mol / L, the concentration of the silver ammonia solution was 0.45 mol / L, and the concentration of the alcohol was above 99.5%.

[0065] A method for preparing a nanogenerator based on branch-stem heterostructure piezoelectric fibers, the preparation flow chart of which is as follows: Figure 1 As shown, the steps are as follows:

[0066] 1.2 g of BCZT-NF@BCZT-SP@Ag prepared in this example was thoroughly stirred with 4.8 g of polyvinylidene fluoride in 30 mL of N,N-dimethylacetamide for 8 hours. The resulting mixture was cast into a composite membrane on a coating machine, which was then encapsulated with electrodes and polyimide to form a PENG.

[0067] Example 4

[0068] A preparation method of a branch-stem heterogeneous structure piezoelectric fiber of this embodiment is shown in the preparation flow chart. Figure 1 As shown, the steps are as follows:

[0069] (1) BCZT-SP was prepared by hydrothermal method using BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate as raw materials. 1.91 g of BaCl2·H2O, 0.16 g of CaCl2, 0.31 g of ZrOCl2·8H2O and 3.23 g of tetrabutyl titanate were uniformly stirred in 100 mL of distilled water and placed in a reactor. An appropriate amount of NaOH was added to the reactor to make BaCl2·H2O and CaCl2·ZrOCl2·8H2O uniformly stirred in 100 mL of distilled water and placed in a reactor. 2+ With OH -The ratio of BCZT to SP is 1:5. The mixed solution in the reactor is reacted at 200℃ for 21 hours, and the obtained material is the synthesized BCZT-SP.

[0070] (2) Ba(OH)2·8H2O, Zr(C5H7O2)4, Ca(OH)2 and tetrabutyl titanate were used as raw materials for preparing BCZT-NF. BCZT-NF@BCZT-SP piezoelectric fibers were prepared by coaxial electrospinning technology. 2.6 g of Ba(OH)2·8H2O, 0.13 g of Ca(OH)2, 0.38 g of Zr(C5H7O2)4 and 3.2 g of tetrabutyl titanate were mixed with 12 mL of acetic acid and 12 mL of ethylene glycol methyl ether to prepare solution 1. 0.35 g of BCZT-SP (0.0016 mol) was mixed with 26 mL of solvent (a mixture of acetic acid, ethylene glycol methyl ether and acetylacetone in a volume ratio of 6:6:1) to prepare solution 2. The viscosity of the solution was adjusted by adding 3 g of polyvinyl pyrrolidone. The sol was prepared into low-moisture preformed fibers using coaxial electrospinning at an 18 kV voltage, a spindle speed of 200 rpm, and an injection flow rate of 20 μL / min. The low-moisture preformed fibers were sintered in a muffle furnace at 780°C for 5 h to obtain BCZT-NF@BCZT-SP piezoelectric fibers.

[0071] (3) Ag nanoparticles were deposited on high surface energy BCZT-SP by chemical reduction to prepare branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). First, 0.3 g of BCZT-NF@BCZT-SP fibers were washed with deionized water and added to a mixed solution of 1.5 mL of SnCl2 and 1 mL of HCl, where the concentration of SnCl2 was 0.07 mol / L and the concentration of HCl was 0.01 mol / L, and stirred for 2 h. Subsequently, the obtained particles were filtered and washed with deionized water and placed in 40 mL of a 0.3 mol / L silver ammonia solution and stirred for 1 h to allow the Ag nanocrystals to coat the surface of the BCZT-NF@BCZT-SP. Finally, 0.54 g of the BCZT-NF@BCZT-SP fiber covered with Ag crystals was placed in a mixed solution consisting of 1.5 mL of formaldehyde solution, 8 mL of silver ammonia solution, and 12 mL of alcohol and stirred for at least 24 h for sufficient reaction to obtain branch-stem heterostructure piezoelectric fibers (BCZT-NF@BCZT-SP@Ag). The concentration of the formaldehyde solution was 0.02 mol / L, the concentration of the silver ammonia solution was 0.3 mol / L, and the concentration of the alcohol was above 99.5%.

[0072] A method for preparing a nanogenerator based on branch-stem heterostructure piezoelectric fibers, the preparation flow chart of which is as follows: Figure 1 As shown, the steps are as follows:

[0073] 0.6 g of BCZT-NF@BCZT-SP@Ag prepared in this example was thoroughly stirred with 2.4 g of polyvinylidene fluoride in 20 mL of N,N-dimethylacetamide for 8 hours. The resulting mixture was cast into a composite membrane on a coating machine, which was then encapsulated with electrodes and polyimide to form a PENG.

[0074] Application Examples

[0075] The PENG prepared by the present invention is used in a monitoring sensor system for a power grid vibration isolation device. Figure 4 Figures 4a and 4b are monitoring and sensing systems for power grid vibration isolation devices based on the PENG of the present invention. The PENG acts as an active sensor to capture the vibration signal of the conductor and transmits it to the computer receiving end for identification and judgment. The system can judge the vibration isolation device according to the vibration status of the transmission line, for example Figure 4 a shows the normal state, Figure 4 b shows an abnormal state (the anti-vibration device fails). Figure 4 ce represents the electrical signals captured by the PENG under three different operating conditions: normal operation of the anti-vibration device, looseness of the anti-vibration device, and failure of the anti-vibration device. Machine learning is then used to determine the three outcomes. The machine learning process involves using a deep learning model to classify one-dimensional time series signals. The data comes from three CSV files with different categories. First, preprocessing is performed by reading the CSV files and converting the data into floating-point format. The data is then normalized using StandardScaler to ensure that each feature has the same scale. After data processing, the data is divided into training and test sets, with 20% of the data used for testing and 80% for training. A simple fully connected neural network (SimpleModel) was constructed using the PyTorch library. The network consists of one input layer, one hidden layer (100 neurons), and an output layer (for the three-class classification task). Training uses the cross-entropy loss function (nn.CrossEntropyLoss) and the Adam optimizer (optim.Adam) with a learning rate of 0.02. The model was trained for 100 cycles, with a training data batch size of 64 per cycle. At the end of each training cycle, the training loss and classification accuracy were recorded. To evaluate the model performance, the test set was used for prediction and the confusion matrix was calculated. To more intuitively display the classification results, a normalized confusion matrix was plotted, showing the classification accuracy of the model for each category. In addition, a loss change graph and classification accuracy curve during the training process were plotted to further verify the training effect of the model ( Figure 4f and 4h). Experimental Results: Through the above experimental steps, we have achieved an effective time series signal classification method. The normalized confusion matrix shows the classification performance of the model between different classes. The classification accuracy and loss curves show that as the training process progresses, the classification performance of the model gradually improves and stabilizes. Figure 4 i shows that the final system judgment accuracy based on the PENG of the present invention can reach more than 95%.

[0076] The present invention effectively improves the electrical output performance of PENG through the microstructural design of piezoelectric fibers, expanding the application scenarios of PENG. By combining the PENG in the present invention with machine learning, a system for abnormal monitoring of anti-vibration devices in power grid transmission lines is designed, which is conducive to the realization of self-powered smart grid sensors and reduces on-site maintenance costs.

[0077] 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 branch-stem heterostructure piezoelectric fiber, characterized in that: Here are the steps: (1) BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate were dissolved in water, and NaOH was added to obtain a mixed solution, and BCZT-SP was prepared by a hydrothermal method; the obtained BCZT-SP and polyvinyl pyrrolidone were dissolved in a solvent to obtain solution 2; (2) Ba(OH)2·8H2O, Ca(OH)2, Zr(C5H7O2)4 and tetrabutyl titanate were dissolved in a mixed solvent of acetic acid and ethylene glycol methyl ether to obtain solution 1; (3) Solution 1 and solution 2 were coaxially electrospun and then sintered to prepare BCZT-NF@BCZT-SP piezoelectric fibers; Solution 1 is the coaxial electrospun inner layer structure solution, and solution 2 is the coaxial electrospun outer layer structure solution; (4) The BCZT-NF@BCZT-SP piezoelectric fiber prepared in step (3) was added to a mixed solution I of SnCl2 and HCl, and the particles obtained after stirring, filtration and cleaning were placed in a silver ammonia solution to obtain BCZT-NF@BCZT-SP with Ag crystals on the surface; The BCZT-NF@BCZT-SP with Ag crystals on its surface was placed in a mixed solution II consisting of formaldehyde solution, silver ammonia solution and alcohol, and stirred to react to obtain branch-stem heterostructure piezoelectric fibers.

2. The preparation method according to claim 1, characterized in that In the step (1), the molar ratio of BaCl2·H2O, CaCl2, ZrOCl2·8H2O and tetrabutyl titanate is (8-9):(1.2-1.6):(0.8-1.1):(9.5-10.5); Ba in the mixed solution 2+ The concentration is 0.07-0.09 mol / L, Ba 2+ With OH - The molar ratio of BCZT-SP is 1:(4-6); the reaction temperature of the hydrothermal method is 190-210°C, and the reaction time is 18-24 h; in solution 2, the solvent is a mixed solvent of acetic acid, ethylene glycol methyl ether and acetylacetone, and the molar concentration of BCZT-SP is 0.04-0.07 mol / L.

3. The preparation method according to claim 2, characterized in that The molar ratio of Ba(OH)2·8H2O, Ca(OH)2, Zr(C5H7O2)4 and tetrabutyl titanate in step (2) is (8-9):(1-2): (0.6-1.2): (9-10), and Ba in solution 1 2+ The concentration is 0.33-0.38 mol / L; the process parameters of the coaxial electrospinning technology in step (3) are: voltage 16-18 kV, roller speed 200-300 rpm, injection flow rate 15-20 μL / min; sintering temperature is 750-800℃, and time is 4-6 h.

4. The preparation method according to claim 3, characterized in that In the step (4), the SnCl2 concentration in the mixed solution I is 0.06-0.08 mol / L, the HCl concentration is 0.01-0.02 mol / L; the concentration of the silver ammonia solution is 0.25-0.45 mol / L; in the step (4), the concentration of the formaldehyde solution in the mixed solution II is 0.02-0.04 mol / L, the concentration of the silver ammonia solution is 0.25-0.45 mol / L, the concentration of the alcohol is above 99.5%, and the volume ratio of the formaldehyde solution, the silver ammonia solution and the alcohol is (1-1.5): (4-8): (8-12); the mass volume ratio of the BCZT-NF@BCZT-SP coated with Ag crystals on the surface to the mixed solution II is 1 g: (35-45) mL.

5. A branch-stem heterostructure piezoelectric fiber prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the branch-stem heterostructure piezoelectric fiber according to claim 5 as a filler in a piezoelectric nanogenerator.

7. A method for preparing a piezoelectric nanogenerator based on a branch-stem heterostructure piezoelectric fiber, characterized in that: Here are the steps: (a) adding the branch-stem heterostructure piezoelectric fiber according to claim 5 and polyvinylidene fluoride to N,N-dimethylacetamide and stirring, and preparing the resulting mixture into a composite film by a casting method; (b) The composite film prepared in step (a) is encapsulated into a piezoelectric nanogenerator via electrodes and polyimide.

8. The piezoelectric nanogenerator obtained by the preparation method according to claim 7.

9. The piezoelectric nanogenerator according to claim 8 is applied to a monitoring sensor system of a power grid vibration isolation device.

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