Flexible piezoelectric composite film, preparation method thereof and application of flexible piezoelectric composite film in running shoes

Abstract

The invention relates to a flexible piezoelectric composite film, a preparation method thereof and application of the flexible piezoelectric composite film in running shoes, and belongs to the technical field of functional electronic materials and application of the functional electronic materials in sports equipment.The flexible piezoelectric composite film is prepared by preparing BF-BT-KNN piezoelectric ceramic with the chemical general formula of xBiFeO3-yBaTiO3-zK [lambda] Na1-[lambda] NbO3, conducting polarization treatment on the BF-BT-KNN piezoelectric ceramic, conducting smashing and grinding on the ceramic piece obtained after polarization treatment, and conducting sintering and sintering on the ceramic piece to obtain the flexible piezoelectric composite film. The flexible piezoelectric composite thin film is prepared by five steps of mixing the thin film with a high-molecular liquid polymer, carrying out ultrasonic treatment on the mixture, and carrying out film forming and curing treatment on the mixture solution after ultrasonic treatment. And the flexible piezoelectric composite film is arranged in the running shoes as a capacitor. The flexible piezoelectric composite film has excellent strain temperature stability, can effectively solve the problem of large material performance fluctuation caused by environment temperature change, and achieves the effect of keeping the performance stability for a long time; meanwhile, the Curie temperature and the high piezoelectric constant are high; and self power supply can be realized for sports equipment such as running shoes.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional electronic materials and their applications in sports equipment, and relates to ferroelectric materials with high electrostrictive performance and high temperature stability and their applications in energy harvesting, adaptive regulation and mechanical feedback systems in sports equipment. In particular, it relates to a flexible piezoelectric composite film, a preparation method thereof and an application in running shoes. Background Art

[0002] Flexible piezoelectric composite materials are a kind of thin film materials that combine piezoelectric materials and flexible substrates, and have the advantages of high sensitivity, good flexibility, light weight and suitability for a variety of application scenarios. Based on the piezoelectric properties of the material itself, the flexible piezoelectric composite film can generate a piezoelectric potential under pressure, thereby generating an electrical signal and realizing a linear conversion between pressure and electrical signal. Compared with traditional brittle piezoelectric ceramics and other traditional piezoelectric materials, the flexible piezoelectric composite film has good flexibility, high impact resistance, fatigue resistance and other advantages, and can be more conveniently applied to small energy harvesting and self-functional wearable devices.

[0003] However, the existing flexible piezoelectric composite films have poor temperature stability, and the material and manufacturing costs are expensive. At the same time, when the existing flexible piezoelectric composite films are applied, a conductive layer (usually aluminum foil) needs to be bonded to their surface for conductive connection with external devices, which will affect the performance of the composite film and is also prone to aluminum foil peeling, affecting the stability of the composite film during use. Summary of the Invention

[0004] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a flexible piezoelectric composite film, a preparation method thereof and an application in running shoes, which are used to solve the technical problem of poor temperature stability of the flexible piezoelectric composite film in the prior art.

[0005] To achieve the above object and other related objects, the present invention provides a preparation method of a flexible piezoelectric composite film, including the following steps:

[0006] S1. Prepare BF-BT-KNN piezoelectric ceramics, and the chemical general formula of the BF-BT-KNN piezoelectric ceramics is xBiFeO3-yBaTiO3-zK λ Na 1-λ NbO3, where x = 0.65 - 0.73, y = 0.2 - 0.4, z = 0.008 - 0.012, λ = 0.1 - 0.9;

[0007] S2. Polarize the BF-BT-KNN piezoelectric ceramics;

[0008] S3. Crush and grind the polarized ceramic sheets and mix them with PDMS polymer;

[0009] S4. After adding a defoaming agent to the mixture, subject the mixture to ultrasonic treatment;

[0010] S5. Subject the ultrasonic-treated mixture solution to film-forming curing treatment to obtain a flexible piezoelectric composite film.

[0011] Preferably in any of the above solutions, the preparation of the BF-BT-KNN piezoelectric ceramic in S1 mainly includes the following steps:

[0012] Step 1: Weigh raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, Nb2O5 according to the stoichiometric ratio of xBiFeO3-yBaTiO3-zK λ Na 1-λ NbO3, and ball-mill the raw materials;

[0013] Step 2: Dry the mixed powder obtained after ball-milling and pre-burn it at 680 - 720 °C for 2 - 3 h;

[0014] Step 3: Add an 8wt% polyvinyl alcohol binder to the pre-burned powder for granulation, and press it into shape to obtain a piezoelectric ceramic green body;

[0015] Step 4: Debind the ceramic green body, with the debinding temperature rising to 550 - 600 °C at a rate of 1 °C / min, and the holding time being 2 - 3 h;

[0016] Step 5: Sinter the debound ceramic green body, with the sintering temperature rising to 1000 - 1010 °C at a rate of 5 °C / min, and the holding time being 2 - 3 h.

[0017] Preferably in any of the above solutions, the chemical formula of the BF-BT-KNN piezoelectric ceramic in S1 is 0.69BiFeO3-0.3BaTiO3-0.01K 0.7 Na 0.3 NbO3.

[0018] Preferably in any of the above solutions, the method for polarizing the BF-BT-KNN piezoelectric ceramic in S2 is to place the BF-BT-KNN piezoelectric ceramic in a 100 °C silicone oil bath and perform polarization treatment at a voltage of 2.5 - 3 kV for 15 - 25 min.

[0019] Preferably in any of the above solutions, in S3, the mass ratio of the ceramic powder to PDMS is 1:1 - 2:1.

[0020] Preferably in any of the above solutions, in S4, after adding 0.05 - 1 ml of defoaming agent to the mixture obtained in S3, place the mixture in an ultrasonic instrument and perform ultrasonic treatment for 8 - 12 min.

[0021] Preferably, in any of the above solutions, in S5, the method of film formation and curing is to keep the mixture solution after ultrasonic treatment at 80 - 120 °C for 30 - 60 min for film formation and curing.

[0022] Preferably, in any of the above solutions, the present invention also discloses a flexible piezoelectric composite film prepared by the above preparation method.

[0023] Preferably, in any of the above solutions, the present invention also discloses the application of the flexible piezoelectric composite film in running shoes, and the prepared flexible piezoelectric composite film is arranged in the running shoes as a capacitor.

[0024] As described above, a flexible piezoelectric composite film, a preparation method thereof, and an application in running shoes according to the present invention have the following beneficial effects:

[0025] 1. The flexible piezoelectric composite film of the present invention has high production efficiency and low material cost, and can be widely applied in sports equipment.

[0026] 2. The flexible piezoelectric composite film of the present invention has high strain temperature stability, can effectively solve the problem of large fluctuations in material performance caused by environmental temperature changes, and thus achieve the effect of long-term performance stability.

[0027] 3. The obtained flexible piezoelectric composite film of the present invention has a high piezoelectric constant, so that the flexible piezoelectric composite film can generate a larger voltage output under the same external force.

[0028] 4. The obtained flexible piezoelectric composite film of the present invention can realize self-power supply for sports equipment such as running shoes, effectively solve the problems that existing sports equipment needs to rely on external power supply, has short battery life and increases the weight of the equipment. At the same time, it can also feedback the force application situation of the exerciser in real time according to the power generation of the flexible piezoelectric composite film, which is convenient for the exerciser to make dynamic adjustments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Shown as BF - BT - K λ N 1-λ XRD pattern of the N ceramic at room temperature.

[0030] Figure 2 Shown as Figure 1 Partial enlarged view of the characteristic diffraction peaks of (110) and (111) in

[0031] Figure 3 For BF - BT - K λ N 1-λ P - E diagram of the N ceramic.

[0032] Figure 4For BF-BT-K λ N 1-λ S-E diagram of N ceramics.

[0033] Figure 5 For BF-BT-K λ N 1-λ Piezoelectric constant diagram of N ceramics.

[0034] Figure 6 Shown as BF-BT-K 0.7 N 0.3 Graph of electrostrictive strain of N ceramics varying with temperature.

[0035] Figure 7 Among them, (a1) is shown as BF-BT-K 0.1 N 0.9 Atomic-resolution STEM HAADF images and fast Fourier transform (FFT) results of N ceramics, (a2) is shown as BF-BT-K 0.7 N 0.3 Atomic-resolution STEM HAADF images and fast Fourier transform (FFT) results of N ceramics.

[0036] Figure 8 Among them, (b1) is BF-BT-K 0.1 N 0.9 Lattice distortion in all directions of N ceramics, (b2) is BF-BT-K 0.7 N 0.3 Lattice distortion in all directions of N ceramics.

[0037] Figure 9 Among them, (c1) is BF-BT-K 0.1 N 0.9 Strain distribution diagrams in all directions of N ceramics, (c2) is BF-BT-K 0.7 N 0.3 Strain distribution diagrams in all directions of N ceramics.

[0038] Figure 10 Among them, (d1) is BF-BT-K 0.1 N 0.9 Rotation diagrams of the local microstructure of N ceramics, (d2) is BF-BT-K 0.7 N 0.3 Rotation diagrams of the local microstructure of N ceramics.

[0039] Figure 11 Shown as BF-BT-K 0.7 N 0.3 Waveform diagram of the electrical energy output signal of N flexible piezoelectric composite films.

[0040] Figure 12It shows a schematic structural diagram of the application of a flexible piezoelectric composite film in running shoes.

[0041] Figure 13 It shows a schematic connection diagram between three power generation components and a micro-capacitor.

[0042] Element number description

[0043] 1 - Power generation component; 2 - Step counter sensor; 3 - GPS locator; 4 - Shoe sole; 5 - Shoe upper; 6 - Insole; 7 - Micro-capacitor. Specific implementation manner

[0044] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0045] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0046] A method for preparing a flexible piezoelectric composite film includes the following steps:

[0047] S1. Prepare BF-BT-KNN piezoelectric ceramics. The chemical general formula of the BF-BT-KNN piezoelectric ceramics is xBiFeO3 - yBaTiO3 - zK λ Na 1-λ NbO3, where x = 0.65 - 0.73, y = 0.2 - 0.4, z = 0.008 - 0.012, λ = 0.1 - 0.9;

[0048] The present invention takes BiFeO3 - BaTiO3 (BF-BT) as the main matrix, introduces a small amount of NaNbO3 into it to obtain a composition of xBiFeO3 - yBaTiO3 - zNaNbO3 (BF-BT-NN), and on this basis, introduces K + to replace Na + and changes the K + / Na + content ratio. Its specific formula is xBiFeO3 - yBaTiO3 - zK λ Na 1-λ NbO3 (BF-BT-K λ N 1-λ N, λ = 0.1 - 0.9).

[0049] Among them, introducing K + (ionic radius ) replaces the A site of the ABO3 perovskite structure, which can further induce lattice distortion and change the macroscopic electrical properties of the material. + The dielectric relaxation properties of the material can be enhanced, thereby enhancing the electrostrain performance.

[0050] At the same time, Na + Smaller radius will cause the lattice to shrink, and K + A larger radius will cause lattice expansion, which can be achieved by adjusting K + / Na + The content ratio can cause different lattice distortions in the local structure and induce local microstress unevenness. The change of local microstress can affect the flipping behavior of the electric domain, thereby regulating the piezoelectric and electrostrain properties and temperature stability.

[0051] Due to K + The ionic radius Bi 3+ The ionic radius Much larger, and Na + The ionic radius with Bi 3+ The ionic radius is similar, but the K + / Na + The ratio will cause different local lattice distortions and generate lattice stress, thereby changing the stress and strain distribution of the lattice.

[0052] By adjusting K + / Na + The ratio can customize different stress distributions, inhibit abnormal grain growth, promote grain densification growth, miniaturize the domain structure, and facilitate domain wall movement and domain flipping.

[0053] BF-BT-KNN piezoelectric ceramics are prepared by solid phase method, and the specific preparation method is as follows:

[0054] Step 1: According to xBiFeO3-yBaTiO3-zK λ Na 1-λ Stoichiometric ratio of NbO3 Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, and Nb2O5, mix the weighed raw materials, put them into a nylon jar, and ball mill them in a planetary ball mill with anhydrous ethanol as the medium for 10 to 12 hours;

[0055] Among them, the purity of Bi2O3, Fe2O3 and BaCO3 is 99%, the purity of TiO2 is 98%, the purity of Na2CO3 is 99.8%, and the purity of K2CO3 and Nb2O5 is 99.5%.

[0056] Step 2: After drying the mixed powder obtained by ball milling at 100 - 150°C, place it in an oxidation furnace crucible and pre-burn it at 680 - 720°C for 2 - 3 hours to complete BF-BT-K λ N 1-λ Solid-phase synthesis of N main crystal phase;

[0057] Step 3: Add 8wt% polyvinyl alcohol (PVA) binder to the pre-burned powder, granulate to obtain granulated powder with good fluidity. Then use a tablet press to press out a disc with a diameter of 10 mm and a thickness of 1 mm under a pressure of 10 Mpa to obtain a piezoelectric ceramic green body;

[0058] Step 4: Debind the ceramic green body. The debinding temperature is raised to 550 - 600°C at a rate of 1°C / min, and the holding time is 2 - 3 hours to remove the binder;

[0059] Step 5: Sinter the debound ceramic green body. The sintering temperature is raised to 1000 - 1010°C at a rate of 5°C / min, and the holding time is 2 - 3 hours to obtain BF-BT-KNN piezoelectric ceramic.

[0060] S2. Polarize the BF-BT-KNN piezoelectric ceramic;

[0061] Specifically, place the BF-BT-KNN piezoelectric ceramic in a 100°C silicone oil bath and polarize it at a voltage of 2.5 - 3 kV for 15 - 25 minutes using a withstand voltage tester;

[0062] S3. Crush and grind the polarized ceramic sheet, and mix it with PDMS polymer in a mass ratio of 1:1 - 2:1;

[0063] S4. Add 0.05 - 1 mL of defoaming agent to the mixture to prevent film bubbles from bulging, and then place the mixture in an ultrasonic instrument for ultrasonic treatment for 8 - 12 minutes;

[0064] S5. Keep the ultrasonic-treated mixture solution at 80 - 120°C for 30 - 60 minutes for film formation and curing to obtain a flexible piezoelectric composite film.

[0065] Correspondingly, the present invention also discloses a flexible piezoelectric composite film prepared by the above method.

[0066] The present invention will be further described below with specific examples:

[0067] Example 1

[0068] Preparation of BF-BT-K 0.1 N 0.9 N piezoelectric ceramic, including the following steps:

[0069] Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, and Nb2O5 according to the stoichiometric ratio of 0.69BiFeO3 - 0.3BaTiO3 - 0.01K 0.1 Na 0.9 NbO3, mix the weighed raw materials, put them into a nylon pot, and ball-mill them in a planetary ball mill for 10 h with absolute ethanol as the medium;

[0070] Step 2: Dry the mixture powder obtained after ball milling, place it in an alumina crucible, and pre-burn it at 680 °C for 3 h;

[0071] Step 3: Add an 8 wt% polyvinyl alcohol binder to the pre-burned powder for granulation, and press it into shape to obtain a piezoelectric ceramic green body;

[0072] Step 4: Place the piezoelectric ceramic green body in a muffle furnace, heat it at a heating rate of 1 °C / min to 550 °C, and keep it warm for 3 h for debinding;

[0073] Step 5: After debinding, heat it at a heating rate of 5 °C / min to 1000 °C, and keep it warm for 3 h to obtain BF-BT-K 0.1 N 0.9 N piezoelectric ceramics.

[0074] Example 2

[0075] Preparation of BF-BT-K 0.3 N 0.7 N piezoelectric ceramics, including the following steps:

[0076] Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, and Nb2O5 according to the stoichiometric ratio of 0.69BiFeO3 - 0.3BaTiO3 - 0.01K 0.3 Na 0.7 NbO3, mix the weighed raw materials, put them into a nylon pot, and ball-mill them in a planetary ball mill for 11 h with absolute ethanol as the medium;

[0077] Step 2: Dry the mixture powder obtained after ball milling, place it in an alumina crucible, and pre-burn it at 700 °C for 2.5 h;

[0078] Step 3: Add an 8 wt% polyvinyl alcohol binder to the pre-burned powder for granulation, and press it into shape to obtain a piezoelectric ceramic green body;

[0079] Step 4: Place the piezoelectric ceramic green body in a muffle furnace, heat it at a heating rate of 1 °C / min to 580 °C, and keep it warm for 2.5 h for debinding;

[0080] Step 5: After debinding, heat at a rate of 5 °C / min to 1005 °C and hold for 3 h to obtain BF-BT-K 0.3 N 0.7 N piezoelectric ceramic.

[0081] Example 3

[0082] Preparation of BF-BT-K 0.5 N 0.5 N piezoelectric ceramic, comprising the following steps:

[0083] Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, Nb2O5 according to the stoichiometric ratio of 0.69BiFeO3-0.3BaTiO3-0.01K 0.5 Na 0.5 NbO3, mix the weighed raw materials and put them into a nylon jar, and ball mill for 11 h in a planetary ball mill with anhydrous ethanol as the medium;

[0084] Step 2: Dry the mixture powder obtained after ball milling, place it in an alumina crucible, and pre-burn at 700 °C for 2 h;

[0085] Step 3: Add 8 wt% polyvinyl alcohol binder to the pre-burned powder for granulation, and press into shape to obtain a piezoelectric ceramic green body;

[0086] Step 4: Place the piezoelectric ceramic green body in a muffle furnace and heat at a rate of 1 °C / min to 580 °C, hold for 2.5 h for debinding;

[0087] Step 5: After debinding, heat at a rate of 5 °C / min to 1008 °C and hold for 2.5 h to obtain BF-BT-K 0.5 N 0.5 N piezoelectric ceramic.

[0088] Example 4

[0089] Preparation of BF-BT-K 0.7 N 0.3 N piezoelectric ceramic, comprising the following steps:

[0090] Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, Nb2O5 according to the stoichiometric ratio of 0.69BiFeO3-0.3BaTiO3-0.01K 0.7 Na 0.3 NbO3, mix the weighed raw materials and put them into a nylon jar, and ball mill for 12 h in a planetary ball mill with anhydrous ethanol as the medium;

[0091] Step 2: Dry the mixture powder obtained after ball milling, place it in an alumina crucible, and pre-bake it at 710 °C for 2 h;

[0092] Step 3: Add 8 wt% polyvinyl alcohol binder to the pre-baked powder for granulation, and press it into shape to obtain a piezoelectric ceramic green body;

[0093] Step 4: Place the piezoelectric ceramic green body in a muffle furnace and heat it to 600 °C at a heating rate of 1 °C / min, and keep it warm for 2 h for debinding;

[0094] Step 5: After debinding is completed, heat it to 1010 °C at a heating rate of 5 °C / min and keep it warm for 2 h to obtain BF-BT-K 0.7 N 0.3 N piezoelectric ceramic.

[0095] Example 5

[0096] Preparation of BF-BT-K 0.9 N 0.1 N piezoelectric ceramic, comprising the following steps:

[0097] Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, Nb2O5 according to the stoichiometric ratio of 0.69BiFeO3-0.3BaTiO3-0.01K 0.9 Na 0.1 NbO3, mix the weighed raw materials and put them into a nylon jar, and ball mill them in a planetary ball mill with absolute ethanol as the medium for 12 h;

[0098] Step 2: Dry the mixture powder obtained after ball milling, place it in an alumina crucible, and pre-bake it at 720 °C for 2 h;

[0099] Step 3: Add 8 wt% polyvinyl alcohol binder to the pre-baked powder for granulation, and press it into shape to obtain a piezoelectric ceramic green body;

[0100] Step 4: Place the piezoelectric ceramic green body in a muffle furnace and heat it to 600 °C at a heating rate of 1 °C / min, and keep it warm for 2 h for debinding;

[0101] Step 5: After debinding is completed, heat it to 1000 °C at a heating rate of 5 °C / min and keep it warm for 3 h to obtain BF-BT-K 0.9 N 0.1 N piezoelectric ceramic.

[0102] Comparative example

[0103] Make the following modifications to the content disclosed in Example 1 or Example 2 or Example 3 or Example 4 or Example 5:

[0104] Without introducing K + , that is, λ = 0, the BF-BT-NN piezoelectric ceramic was prepared.

[0105] The piezoelectric ceramics prepared in the above examples and comparative examples were tested for electrical properties:

[0106] Figure 1 is the XRD pattern of BF-BT-K λ N 1-λ N ceramics at room temperature. It can be seen that all samples exhibited a typical perovskite structure without impurity phases.

[0107] Figure 2 is Figure 1 the partial enlarged view of the (110) and (111) characteristic diffraction peaks in

[0108] From Figure 1 and Figure 2 it can be seen that as the larger-radius K + gradually replaces the smaller-radius Na + except for the narrowing of the characteristic peaks, the peak position did not shift significantly to a smaller angle, indicating that the introduction of a small amount of K + might only cause local lattice distortion and did not increase the average interplanar spacing.

[0109] Figure 3 It can be seen that at the same electric field strength, as the K + content increases and the Na + content decreases, the polarization effect of the BF-BT-K λ N 1-λ N piezoelectric ceramic enhances. When the K + content reaches 0.7, the polarization effect of the BF-BT-K λ N 1-λ N piezoelectric ceramic reaches the maximum; while when the K + content is 0.9, the polarization effect of the BF-BT-K λ N 1-λ N piezoelectric ceramic gradually decreases.

[0110] Figure 4 It can be seen that at the same electric field strength, as the K + content increases and the Na + content decreases, the strain of the BF-BT-K λ N 1-λ N piezoelectric ceramic gradually increases. When the K + content reaches 0.7, the strain of the BF-BT-K λ N 1-λ N piezoelectric ceramic reaches the maximum; while when the K +When the content is 0.9, BF-BT-K λ N 1-λ The strain of the N piezoelectric ceramic gradually decreases. K + Substitution can effectively enhance the unipolar strain response, and when λ = 0.7 (BF-BT-K 0.7 N 0.3 N, S~>0.25%), it reaches the maximum value, which is 34.2% higher than that of BF-BT-NN (λ = 0) ceramics.

[0111] Figure 5 It can be seen that as the K + content increases and the Na + content decreases, the piezoelectric constant of the BF-BT-K λ N 1-λ N piezoelectric ceramic gradually increases. When the K + content reaches 0.7, the piezoelectric constant of the BF-BT-K λ N 1-λ N piezoelectric ceramic reaches the maximum, which is 8.69% higher than that of BF-BT-NN (λ = 0) ceramics.

[0112] Figure 6 It can be known that the BF-BT-K λ N 1-λ N ceramic has high strain temperature stability.

[0113] Figure 7 In the STEM HAADF image, the atomic-scale structure of the ceramic is directly presented, while the FFT pattern converts the lattice information in real space into reciprocal space and can be used to determine the microstructural information within the lattice. By adjusting the K + / Na + ratio, different lattice distortions of the local structure can be generated, and local microstress inhomogeneity can be induced.

[0114] Figure 8 From the distorted GPA results in (b1) and (b2), it can be seen that the lattice distortions in all directions of BF-BT-K 0.7 N 0.3 N are more significant than those of BF-BT-K 0.1 N 0.9 N. Among them, e xx and e yy respectively represent the positive distortions along the x and y directions, and e xy and e yx represent the distortions in the shear direction.

[0115] Figure 9 It can be seen that BF-BT-K 0.7 N 0.3The strain state distribution of N ceramics is more uneven, indicating that the stress non-uniformity in the microstructure is significantly enhanced. This lattice distortion formed by the change of the K + / Na + ratio causes structural and stress non-uniformity at the atomic scale, enhancing the micro-stress inside the structure.

[0116] Figure 10 In, ω xy and ω yx describe the in-plane rotation of the ceramics, revealing the rotation characteristics of the micro-regions inside the sample.

[0117] The change of micro-stress can affect the flipping behavior of electric domains, thereby regulating the piezoelectric and electrostrictive strain properties and their temperature stability. Through comprehensive Figures 7 - 10 analysis, it can be known that the uneven distribution of lattice stress will significantly affect the intrinsic properties of functional materials. The introduction of K + results in an uneven distribution of the stress field, generating a large local stress-strain energy and increasing the system energy. To reduce the system energy, the stress interacts with the domains, and the strain energy provides part of the energy for the miniaturization of the domains. In addition, when the domains flip under the action of an external electric field, the strain energy further releases energy to promote the switching of the domains.

[0118] Example 6

[0119] Using the BF-BT-K λ N 1-λ N piezoelectric ceramic material prepared in Example 1 or Example 2 or Example 3 or Example 4 or Example 5 to prepare a flexible piezoelectric composite film, including the following steps:

[0120] S1. Polarize the BF-BT-KNN piezoelectric ceramic;

[0121] Specifically, place the BF-BT-KNN ceramic in a silicone oil bath at 100 °C and polarize it for 25 min under a voltage of 2.5 kV using a withstand voltage tester;

[0122] S2. Crush and grind the polarized ceramic sheet and mix it with the PDMS polymer in a mass ratio of 1:1;

[0123] S3. Add 0.05 mL of defoamer to the mixture to prevent film bubbles from bulging, and then place the mixture in an ultrasonic instrument for ultrasonic treatment for 12 min;

[0124] S4. Keep the ultrasonic-treated mixture solution at 80 °C for 60 min for film forming and curing to obtain a flexible piezoelectric composite film.

[0125] Test the performance of the prepared flexible piezoelectric composite film:

[0126] Figure 11 When λ = 0.7, it is the waveform diagram of the electrical energy output signal of the flexible piezoelectric composite film. It can be seen that the output voltage of the flexible piezoelectric composite film is relatively high and has good stability.

[0127] Example 7

[0128] Application of the flexible piezoelectric composite film in running shoes. The prepared flexible piezoelectric composite film is set in the running shoes as a capacitor. As Figure 12 shown, specifically:

[0129] The running shoes include a sole 4, an upper 5, and an insole 6 disposed between the sole 4 and the upper 5. Three groups of power generation components 1 are arranged along the length direction of the sole 4 between the sole 4 and the insole 6. The three groups of power generation components 1 are respectively disposed at the front foot section, the mid-foot section, and the rear foot section. Each group of power generation components 1 includes a plurality of flexible piezoelectric composite films arranged side by side, and the flexible piezoelectric composite films are bonded to the upper surface of the sole 4. The three groups of power generation components 1 are connected to a micro-capacitor 7, and the micro-capacitor 7 is disposed inside the sole 4. A step counter sensor 2 and a GPS locator 3 are further provided between the sole 4 and the insole 6, and the step counter sensor 2 and the GPS locator 3 are respectively connected to the micro-capacitor 7, wherein the step counter sensor 2 is used to calculate the number of steps, kilometers, and calories consumed, etc.

[0130] The mechanical energy when a runner steps on the flexible piezoelectric composite film during walking or running is converted into electrical energy under the action of the flexible piezoelectric composite film and stored in the micro-capacitor 7 to supply power to the step counter sensor 2 and the GPS locator 3, thereby realizing the self-power supply of the running shoes, avoiding relying on external power supply, increasing the battery life while reducing the weight of the shoes.

[0131] In this embodiment, the flexible piezoelectric composite film in the power generation component 1 has high-stability electrostrictive strain performance, and the performance fluctuation of the flexible piezoelectric composite film with the change of ambient temperature is small, so as to effectively reduce the influence of ambient temperature on the power generation performance of the flexible piezoelectric composite film, and ensure that the flexible piezoelectric composite film can stably generate electrical energy under different ambient temperatures and different temperature states of the human foot (i.e., inside the shoe) at the same ambient temperature, thereby ensuring the effective and stable use of the step counter sensor 2 and the GPS locator 3.

[0132] As Figure 13As shown, the three groups of power generation components 1 and the micro-capacitor 7 are respectively connected with an energy collection module and an electricity quantity detection module in sequence. At the same time, the running shoes also include a terminal, which can be set in electronic products such as mobile phones and sports watches. A data analysis module is arranged in the terminal. The three electricity quantity detection modules are respectively electrically connected to the data analysis module, and the three electricity quantity detection modules respectively detect the amount of electricity generated by the forefoot, the middle foot and the rear foot during exercise and transmit it to the data analysis module for data analysis, so that the athlete can infer the focus point, exercise state, etc. during exercise according to the amount of electricity generated by the front, middle and rear sections of the foot, so as to facilitate dynamic adjustment according to the exercise data, thereby improving the safety and effectiveness of exercise.

[0133] At the same time, the flexible piezoelectric composite material in this embodiment as a self-powered device can also improve the wearing comfort due to its good flexibility.

[0134] Of course, the flexible piezoelectric composite film is not limited to being used as a self-powered device in running shoes, but can also be used in other equipment that requires self-power, such as setting the flexible piezoelectric composite film in table tennis rackets, footballs, basketballs, etc.

[0135] In summary, the flexible piezoelectric composite film of the present invention has high strain stability, which can effectively solve the problem of large fluctuations in material performance due to changes in ambient temperature, thereby achieving the effect of maintaining performance stability for a long time. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

[0136] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a flexible piezoelectric composite film, characterized in that, It includes the following steps: S1. Prepare BF-BT-KNN piezoelectric ceramics. The chemical general formula of the BF-BT-KNN piezoelectric ceramics is xBiFeO3-yBaTiO3-zK λ Na 1-λ NbO3, where x = 0.65 - 0.73, y = 0.2 - 0.4, z = 0.008 - 0.012, and λ = 0.1 - 0.9; S2. Polarize the BF-BT-KNN piezoelectric ceramic; S3. Crush and grind the polarized ceramic sheet and mix it with the PDMS polymer; S4. Add a defoaming agent to the mixture and then perform ultrasonic treatment on the mixture; S5. Perform film-forming and curing treatment on the ultrasonic-treated mixture solution to obtain a flexible piezoelectric composite film.

2. The preparation method of the flexible piezoelectric composite film according to claim 1, characterized in that The preparation of the BF-BT-KNN piezoelectric ceramic in S1 mainly includes the following steps: Step 1: Weigh the raw materials Bi2O3, Fe2O3, BaCO3, TiO2, Na2CO3, K2CO3, and Nb2O5 according to the stoichiometric ratio of xBiFeO3 - yBaTiO3 - zK λ Na 1-λ NbO3, and ball - mill the raw materials; Step 2: Dry the mixed powder obtained after ball milling and pre-burn it at 680-720 °C for 2-3 h; Step 3: Add an 8wt% polyvinyl alcohol binder to the pre-burned powder for granulation and press it into shape to obtain a piezoelectric ceramic green body; Step 4: Debind the ceramic green body, with the debinding temperature rising to 550-600 °C at a rate of 1 °C / min and the holding time being 2-3 h; Step 5: Sinter the debound ceramic green body, with the sintering temperature rising to 1000-1010 °C at a rate of 5 °C / min and the holding time being 2-3 h.

3. The method for preparing a flexible piezoelectric composite film according to claim 1, characterized in that, The chemical formula of the BF-BT-KNN piezoelectric ceramic in S1 is 0.69BiFeO3 - 0.3BaTiO3 - 0.01K 0.7 Na 0.3 NbO3.

4. The method for preparing a flexible piezoelectric composite film according to claim 1, characterized in that, The method for polarizing the BF-BT-KNN piezoelectric ceramic in S2 is to place the BF-BT-KNN piezoelectric ceramic in a 100 °C silicone oil bath and perform polarization treatment at a voltage of 2.5-3 kV for 15-25 min.

5. The method for preparing a flexible piezoelectric composite film according to claim 1, wherein In S3, the mass ratio of the ceramic powder to PDMS is 1:1-2:

1.

6. The method for preparing the flexible piezoelectric composite film according to claim 1, wherein In S4, add 0.05-1 mL of defoaming agent to the mixture obtained in S3 and then place the mixture in an ultrasonic instrument for ultrasonic treatment for 8-12 min.

7. The preparation method of the flexible piezoelectric composite film according to claim 1, characterized in that, In S5, the method for film-forming and curing is to keep the ultrasonic-treated mixture solution at 80-120 °C for 30-60 min for film-forming and curing.

8. A flexible piezoelectric composite film, characterized in that: Prepared by the preparation method according to any one of claims 1-7.

9. The application of the flexible piezoelectric composite film according to claim 8 in running shoes, characterized in that: The prepared flexible piezoelectric composite film is set in the running shoes as a capacitor.

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