A piezoelectric nanogenerator, a preparation method thereof, and a wireless sensing system

Abstract

The present invention provides a piezoelectric nanogenerator based on coaxial heterostructured composite piezoelectric fibers, a preparation method, and a wireless sensing system. This preparation method involves coating the surface of BT with a layer of Ag nanoparticles, spinning the fibers using a coaxial needle, and finally producing a PENG (Peng). This method increases the effective polarization voltage of the piezoelectric particles during polarization and enhances stress transfer within the particles. This method exhibits high piezoelectric output performance, enabling the application of PENG in wireless sensing systems and scalable industrial applications.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic devices, and in particular to a piezoelectric nanogenerator and a preparation method thereof, and a wireless sensing system based on the piezoelectric nanogenerator. Background Art

[0002] With the increasing prevalence of the Internet of Things (IoT) in everyday life, new demands are being placed on the energy supply of the sensors, portable, and embedded electronic devices involved. The goal is for power supply devices to be portable, sustainable, and maintenance-free. However, these devices are still primarily powered by traditional batteries. The associated issues of battery replacement and disposal not only create significant inconvenience in device use and maintenance but also pose environmental risks, contradicting popular design ideals. Therefore, developing small, lightweight, self-driving nanodevices that can absorb energy from the surrounding environment and convert it into electricity has become one of the best options for addressing this energy supply issue.

[0003] Flexible piezoelectric nanogenerators (PENGs) based on organic / inorganic composite materials are devices that convert mechanical energy into electrical energy through the piezoelectric effect. Inorganic piezoelectric materials such as BaTiO3, PbZrTiO3, and ZnSnO3 possess excellent piezoelectric properties, while organic materials such as polyvinylidene fluoride (PVDF) and polydimethylsiloxane (PDMS) offer low density, good flexibility, and easy processing. Combining these two materials is a simple and effective method for fabricating flexible PENGs. These PENGs can respond to complex conditions such as bending, torsion, and stretching, meeting the needs of wearable / embedded devices of varying shapes. They can also harvest low-frequency mechanical energy generated by factors such as human walking, muscle stretching, mechanical vibration, and air flow.

[0004] Prior art uses electrospinning technology to fabricate PENGs based on organic / inorganic composite materials. The polarization and stress transfer processes significantly influence the PENG's piezoelectric output. In this technique, inorganic piezoelectric particles are encapsulated in an organic polymer. Since the organic material is typically an insulating polymer, while the inorganic piezoelectric material is typically a semiconductor, the organic material consumes most of the polarization voltage during the polarization process, leaving the actual polarization voltage acting on the inorganic piezoelectric particles very small. Furthermore, during stress transfer, when an external force is applied to the PENG, the flexible polymer material dissipates most of the force, resulting in a low level of stress actually transferred to the piezoelectric particles. Consequently, these deficiencies in the polarization and stress transfer processes in prior art lead to relatively low PENG output performance. Summary of the Invention

[0005] In response to the defects of low PENG output performance caused by low effective polarization electric field of piezoelectric particles and low stress transfer efficiency in the existing technology, the present invention provides a method for preparing a piezoelectric nanogenerator based on coaxial heterostructure composite piezoelectric fibers, a piezoelectric nanogenerator prepared by this method and a wireless sensing system based on the piezoelectric nanogenerator. The piezoelectric nanogenerator provided by the present invention can provide higher piezoelectric output.

[0006] A first aspect of the present invention provides a method for preparing a piezoelectric nanogenerator based on a coaxial heterostructure composite piezoelectric fiber, characterized in that it comprises the following steps:

[0007] S1: Barium titanate (BT) nanoparticles were added to a mixed solution of SnCl2 and HCl, and stirred for 1 hour, wherein the SnCl2 concentration was 0.08 mol / L and the HCl concentration was 0.01 mol / L;

[0008] S2: washing the barium titanate (BT) particles prepared in step S1 with purified water and then adding them to a silver ammonia solution, stirring for 1-2 hours to deposit Ag nanocrystals on the surface of the barium titanate (BT) nanoparticles, wherein the concentration of the silver ammonia solution is 0.3-0.5 mol / L;

[0009] S3: placing barium titanate (BT) particles coated with Ag crystallites in a mixed solution consisting of 1.5 mL of formaldehyde solution, 4-8 mL of silver ammonia solution, and 8.5-12.5 mL of alcohol, and stirring for at least 12 hours for sufficient reaction to obtain barium titanate (BT) piezoelectric particles coated with Ag nanospheres, wherein the formaldehyde solution has a concentration of 0.03-0.06 mol / L, the silver ammonia solution has a concentration of 0.3-0.5 mol / L, and the alcohol concentration is 99.7%;

[0010] S4: Prepare a solution a by mixing 3 ml of N,N-dimethylformamide and 7 ml of acetone solution, taking 1 g of polyvinylidene fluoride (PVDF) and 0.25 g of barium titanate (BT) coated with Ag nanospheres, mixing with the solvent, and stirring for at least 12 hours;

[0011] S5: Prepare a solvent of 3 ml N,N-dimethylformamide and 7 ml acetone solution, take 1 g of polyvinylidene fluoride (PVDF) and 0.25 g of barium titanate (BT), mix with the above solvent, and stir for at least 12 hours to prepare solution b;

[0012] S6: placing the prepared solution a and solution b into syringe a and syringe b respectively, and performing a spinning preparation process using a coaxial needle, wherein solution a is the coaxial inner layer and solution b is the coaxial outer layer;

[0013] S7: The prepared spun fiber membrane is added with electrodes and then encapsulated in polyimide plastic, leaving the upper and lower electrode wires, thereby preparing a piezoelectric nanogenerator (PENG).

[0014] Preferably, the barium titanate (BT) has a specification of nanopowder, <100 nm particlesize (BET), ≥99% trace metals basis.

[0015] Preferably, the specification of the polyvinylidene fluoride (PVDF) is an average Mw of 275,000 by GPC and an average Mn of 107,000, pellets.

[0016] Preferably, the spinning voltage is 18 kV, the rotation speed of the collecting rod is 200 rpm, the distance between the coaxial needle and the collecting rod is 15 cm, and the pushing speed of the syringe is 20 μl / min.

[0017] Preferably, the Ag coated on the surface of barium titanate (BT) is 6 nm and is evenly distributed.

[0018] Preferably, in the coaxial heterostructure composite piezoelectric fiber, the four main elements Ba, Ti, O and Ag are evenly distributed.

[0019] The second aspect of the present invention provides a piezoelectric nanogenerator obtained by the above preparation method.

[0020] A third aspect of the present invention provides a self-driven soil moisture wireless sensing system using the above-mentioned piezoelectric nanogenerator, characterized in that the self-driven soil moisture wireless sensing system collects wind energy to power the sensing system, and the system includes a chip, a Bluetooth module and a four-wire soil moisture sensor.

[0021] Preferably, the chip is an STM32F103C8T6 chip, the Bluetooth module is an HC-05 Bluetooth module, and the four-wire soil moisture sensor is an ELECFANS four-wire soil moisture sensor.

[0022] Preferably, the piezoelectric nanogenerator is connected to the STM32F103C8T6 chip through a rectifier circuit, the Vcc, RXD, and TXD pins of the HC-05 Bluetooth module are respectively connected to the Vdd1, PA9, and PA10 pins of the STM32F103C8T6 chip, and the pins Vcc and A0 of the ELECFANS four-wire soil moisture sensor are respectively connected to the pins Vdd2 and PA1 of the STM32F103C8T6 chip.

[0023] The present invention first uses a chemical seeding reduction method to coat the surface of BT with a layer of Ag nanoparticles. BT and the Ag-coated BT are then mixed and stirred with a PVDF polymer to form two solutions, a and b. These solutions are then placed in two syringes and spun using coaxial needles, with solution a forming the inner coaxial layer and solution b forming the outer coaxial layer. The resulting spun fiber membrane is then coated with electrodes and encapsulated in polyimide plastic, leaving the upper and lower electrode conductors free. This completes the PENG. The present invention has the following beneficial effects: Because Ag is a conductive material, the outer layer of Ag attached to the BT surface enhances the local polarization electric field, thereby increasing the effective polarization voltage of the piezoelectric particles during polarization. Furthermore, the core-shell structure, in which a layer of Ag nanoparticles is coated on the BT surface, enhances stress transfer between the piezoelectric particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention discloses a preparation process of a piezoelectric nanogenerator based on coaxial heterostructure composite piezoelectric fibers.

[0025] Figure 2 TEM image of piezoelectric particles.

[0026] Figure 3 X-ray diffraction patterns of atomic components and piezoelectric particles.

[0027] Figure 4 Comparison of efficiency differences during polarization and stress transfer simulated using COMOSL software.

[0028] Figure 5 The present invention relates to a self-driven soil moisture wireless sensing system implemented using the PENG of the present application. DETAILED DESCRIPTION

[0029] The present invention will be further described below with reference to the embodiments.

[0030] Example 1:

[0031] like Figure 1 As shown, the preparation process of the piezoelectric nanogenerator based on the coaxial heterostructure composite piezoelectric fiber of the present invention is as follows:

[0032] S1: Add barium titanate (BT) nanoparticles to a mixed solution of SnCl2 and HCl, and stir for 1 hour, wherein the SnCl2 concentration is 0.08 mol / L and the HCl concentration is 0.01 mol / L. The barium titanate (BT) specification is nanopowder, <100 nm particle size (BET), ≥99% trace metal basis.

[0033] S2: The barium titanate (BT) particles prepared in step S1 are washed with purified water and then added to a silver ammonia solution, and stirred for 1 hour to deposit Ag nanocrystals on the surface of the barium titanate (BT) nanoparticles, wherein the concentration of the silver ammonia solution is 0.3 mol / L; Figure 1 (b) shows BT coated with Ag nanocrystals obtained by chemical seeding method.

[0034] S3: placing barium titanate (BT) particles coated with Ag crystallites in a mixed solution consisting of 1.5 mL of formaldehyde solution, 4 mL of silver ammonia solution, and 8.5 mL of alcohol, and stirring for 12 hours for sufficient reaction to obtain barium titanate (BT) piezoelectric particles coated with Ag nanospheres, wherein the concentration of the formaldehyde solution is 0.04 mol / L, the concentration of the silver ammonia solution is 0.3 mol / L, and the concentration of the alcohol is 99.7%; Figure 1 (c) is a schematic diagram of BT piezoelectric particles coated with Ag nanospheres obtained after Ag crystal growth.

[0035] Figure 2 (a) and Figure 2 (b) Transmission electron microscope (TEM) images of BT particles and BT particles coated with Ag, respectively. The Ag coated on the BT surface is about 6 nm and is evenly distributed. Figure 2 (c) is a high-definition TEM image of Ag, whose lattice spacing of 0.203nm and 0.231nm corresponds to the (200) and (100) orientation structures of Ag, respectively.

[0036] Figure 3 (a) is the atomic composition ratio of the four elements, of which Ag accounts for about 8.76%, and the four elements are evenly distributed; Figure 3(b) is the X-ray diffraction pattern of BT particles and coated with Ag, where 2θ of 21.9°, 31.7°, 38.1°, 45.0°, 55.9°, and 65.5° correspond to the characteristic peaks of BT (100), (110), (111), (200), (211), and (220), respectively, while 38.5° and 44.2° correspond to the characteristic peaks of face-centered cubic structure Ag (111), (200), (220), and (311).

[0037] S4: Prepare a solution a by mixing 3 ml of N,N-dimethylformamide and 7 ml of acetone solution into a solvent, taking 1 g of polyvinylidene fluoride (PVDF) and 0.25 g of barium titanate (BT) coated with Ag nanospheres, mixing with the solvent, and stirring for 12 hours; the polyvinylidene fluoride (PVDF) has an average Mw of 275,000 by GPC and an average Mn of 107,000 pellets.

[0038] S5: Prepare a solvent of 3 ml N,N-dimethylformamide and 7 ml acetone solution, take 1 g of polyvinylidene fluoride (PVDF) and 0.25 g of barium titanate (BT), mix with the above solvent and stir for 12 hours to prepare solution b; Figure 1 (d) shows the process of obtaining solution a and solution b; the specification of the polyvinylidene fluoride (PVDF) is average Mw ~ 275,000 by GPC, average Mn ~ 107,000, pellets.

[0039] S6: placing the prepared solution a and solution b into syringe a and syringe b respectively, and performing a spinning preparation process using a coaxial needle, wherein solution a is the coaxial inner layer and solution b is the coaxial outer layer; Figure 1 (e) shows the coaxial electrospinning process, in which the spinning voltage is set to 18 kV, the collecting rod speed is 200 rpm, the distance between the coaxial needle and the collecting rod is 15 cm, and the syringe pushing speed is 20 μl / min.

[0040] S7: The prepared spun fiber membrane is added with electrodes and then encapsulated in polyimide plastic, leaving the upper and lower electrode wires, thereby preparing a piezoelectric nanogenerator (PENG). Figure 1 (f) in FIG. 3 shows the final PENG.

[0041] Figure 4 The efficiency difference in the polarization and stress transfer process between the conventional piezoelectric fiber membrane and the piezoelectric fiber membrane of the present invention is simulated using COMOSL software. Figure 4 Figure a shows the polarization voltage simulation of a piezoelectric fiber (a-I) prepared by a conventional process and a piezoelectric fiber (a-II) prepared by the present invention under the same polarization conditions. It can be seen that the present invention can significantly improve the polarization voltage distribution acting on the piezoelectric filler. Figure 4 b is the stress transfer simulation of the above two PENGs under an external force of 30 N. The results show that the structure designed in the present invention is more conducive to improving the stress transfer efficiency between piezoelectric fillers. Figure 4 c is the piezoelectric potential finally generated by the two PENGs on the surface. The results also show that the structure designed by the present invention will produce a larger piezoelectric output.

[0042] Example 2:

[0043] like Figure 5 As shown in the figure, a self-driven wireless soil moisture sensing system is implemented using the PENG based on Example 1. The self-driven wireless soil moisture sensing system collects wind energy to power the sensing system and transmits the measured temperature and humidity data to a mobile phone for monitoring. The system includes a chip, a Bluetooth module, and a four-wire soil moisture sensor. Figure 5 (a) is a physical photo of the system.

[0044] The chip is an STM32F103C8T6 chip, the Bluetooth module is an HC-05 Bluetooth module, and the four-wire soil moisture sensor is an ELECFANS four-wire soil moisture sensor. Figure 5 (b) Shows the STM32F103C8T6 chip, HC-05 Bluetooth module and ELECFANS four-wire soil moisture sensor components in the system.

[0045] Figure 5 (c) shows the specific circuit connection method. The piezoelectric nanogenerator is connected to the STM32F103C8T6 chip through a rectifier circuit. The Vcc, RXD, and TXD pins of the HC-05 Bluetooth module are connected to the Vdd1, PA9, and PA10 pins of the STM32F103C8T6 chip, respectively. The Vcc and A0 pins of the ELECFANS four-wire soil moisture sensor are connected to the Vdd2 and PA1 pins of the STM32F103C8T6 chip, respectively.

[0046] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0047] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for preparing a piezoelectric nanogenerator based on coaxial heterostructure composite piezoelectric fibers, characterized in that: The following steps are involved: S1: adding barium titanate nanoparticles to a mixed solution of SnCl2 and HCl, and stirring for 1 hour, wherein the SnCl2 concentration is 0.08 mol / L and the HCl concentration is 0.01 mol / L; S2: washing the barium titanate particles in step S1 with purified water and then adding them to a silver ammonia solution, stirring for 1-2 hours to allow Ag nanocrystals to be deposited on the surface of the barium titanate nanoparticles, wherein the concentration of the silver ammonia solution is 0.3-0.5 mol / L; S3: placing the barium titanate particles with Ag crystallites on their surfaces in a mixed solution consisting of 1.5 mL of formaldehyde solution, 4-8 mL of silver ammonia solution, and 8.5-12.5 mL of alcohol, and stirring for at least 12 hours for sufficient reaction, thereby obtaining barium titanate piezoelectric particles with Ag nanospheres on their surfaces; wherein the concentration of the formaldehyde solution is 0.03-0.06 mol / L, the concentration of the silver ammonia solution is 0.3-0.5 mol / L, and the concentration of the alcohol is 99.7%; S4: Prepare a solution a by mixing 3 ml of N,N-dimethylformamide and 7 ml of acetone solution, taking 1 g of polyvinylidene fluoride and 0.25 g of barium titanate coated with Ag nanospheres, mixing with the solvent, and stirring for at least 12 hours; S5: Prepare a solution b by mixing 3 ml of N,N-dimethylformamide and 7 ml of acetone solution, taking 1 g of polyvinylidene fluoride and 0.25 g of barium titanate, mixing with the above solvent, and stirring for at least 12 hours; S6: placing the prepared solution a and solution b into syringe a and syringe b respectively, and performing a spinning preparation process using a coaxial needle, wherein solution a is the coaxial inner layer and solution b is the coaxial outer layer; S7: The prepared spun fiber membrane is added with electrodes and then encapsulated in polyimide plastic, leaving the upper and lower electrode wires, thereby preparing a piezoelectric nanogenerator.

2. The method for preparing a piezoelectric nanogenerator according to claim 1, wherein: The barium titanate is in the form of nanoparticles, with a particle size of <100 nm as measured by the BET method and a purity of ≥99% based on trace metals.

3. The method for preparing a piezoelectric nanogenerator according to claim 2, wherein: The polyvinylidene fluoride has a weight average molecular weight of 275,000 and a number average molecular weight of 107,000 as measured by GPC, and is in a granular form.

4. The method for preparing a piezoelectric nanogenerator according to claim 3, wherein: The spinning voltage was 18 kV, the collecting rod speed was 200 rpm, the distance between the coaxial needle and the collecting rod was 15 cm, and the syringe pushing speed was 20 μl / min.

5. The method for preparing a piezoelectric nanogenerator according to claim 4, wherein: The Ag coated on the surface of barium titanate is 6 nm and is evenly distributed.

6. The method for preparing a piezoelectric nanogenerator according to claim 1, wherein: In the coaxial heterostructure composite piezoelectric fiber, four main elements, Ba, Ti, O, and Ag, are evenly distributed.

7. A piezoelectric nanogenerator obtained by the preparation method of a piezoelectric nanogenerator based on coaxial heterostructure composite piezoelectric fibers according to claim 1.

8. A self-driven soil moisture wireless sensing system based on the piezoelectric nanogenerator according to claim 7, characterized in that: The self-driven soil moisture wireless sensing system collects wind energy to power the sensing system. The system includes a chip, a Bluetooth module and a four-wire soil moisture sensor.

9. The self-driven soil moisture wireless sensing system according to claim 8, wherein: The chip is an STM32F103C8T6 chip, the Bluetooth module is an HC-05 Bluetooth module, and the four-wire soil moisture sensor is an ELECFANS four-wire soil moisture sensor.

10. The self-driven soil moisture wireless sensing system according to claim 9, wherein: The piezoelectric nanogenerator is connected to the STM32F103C8T6 chip through a rectifier circuit. The Vcc, RXD, and TXD pins of the HC-05 Bluetooth module are respectively connected to the Vdd1, PA9, and PA10 pins of the STM32F103C8T6 chip. The Vcc and A0 pins of the ELECFANS four-wire soil moisture sensor are respectively connected to the Vdd2 and PA1 pins of the STM32F103C8T6 chip.

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