Structurally adjustable flexible nylon 11 piezoelectric separation fiber membrane, preparation method and application

Abstract

The application discloses a structure-adjustable flexible nylon 11 piezoelectric separation fiber membrane and a preparation method and application thereof. The specific preparation method is as follows: (1) nylon 11 particles and inorganic nano fillers are added into a cosolvent system to react, and a homogeneous matrix solution A is prepared; (2) nylon 11 particles and polyethylene glycol are added into the cosolvent system to react, and a homogeneous matrix solution B is prepared; (3) the homogeneous matrix solutions A and B are defoamed, and then coaxial electrospinning is performed to form a membrane, and a structure-adjustable flexible nylon 11 piezoelectric separation fiber membrane is prepared. The application has the advantages of simple technology, flexibility, light weight, variable and controllable structure, adjustable piezoelectric active crystal phase, and high force-electricity output performance, effectively solves the problems of limited mechanical properties, poor flexibility, easy folding, large volume ratio, uncontrollable structure, low force-electricity output and the like of existing materials, and has great potential application prospect in energy storage equipment, emergency energy supply and micro intelligent wearable energy system.

Description

Technical Field

[0001] This invention belongs to the field of energy harvesting materials and energy storage battery devices, specifically relating to a flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure, its preparation method and application, mainly used in energy harvesting devices, energy storage batteries, emergency energy supply and micro-miniature smart wearable energy systems. Background Technology

[0002] Nylon 11, the most studied member of the odd-numbered nylon family, is a promising functional material for future electronic devices and energy storage systems. However, nylon 11 prepared by conventional methods such as coating, casting, and unidirectional / biaxial stretching is mostly in the form of two-dimensional structures such as planar films or bulk materials, which cannot fully utilize its effective piezoelectric output properties. Therefore, structural optimization or the design of higher-dimensional structural materials is crucial.

[0003] Electrospinning technology can be used to fabricate one-, two-, and three-dimensional structural devices, offering advantages such as simple operation, controllable conditions, and low cost. Furthermore, fiber structures, such as porous or hollow structures, can be adjusted and fiber properties optimized through precise control of spinning conditions and post-electrospinning treatments, thereby achieving customized applications. However, the formation of the most stable non-piezoelectric / ferroelectric α phase is inevitable during the electrospinning process of Nylon 11 fibers.

[0004] The development of flexible power sources is a promising strategy for solving the problem of wearable electronic devices operating without a power source or charging base. A flexible self-charging battery is an energy storage device that simultaneously collects and stores energy through force-to-electricity conversion via the piezoelectric effect. The piezoelectric diaphragm has a dual function: firstly, it acts as a separator to prevent short circuits; secondly, it serves as a piezoelectric electrolyte, providing a piezoelectric potential in the internal circuit to drive ion migration and achieve self-charging. Currently, there are no research reports on the use of nylon 11 in flexible self-charging batteries. Summary of the Invention

[0005] To address the aforementioned shortcomings in existing technologies, this invention provides a flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure, its preparation method, and its applications. This invention has the advantages of simple technology, flexibility and lightweight, variable and controllable structure, controllable piezoelectric active crystal phase, high electromechanical output performance, and portable self-powered operation. The prepared flexible self-charging battery has great potential application prospects in energy storage devices, emergency energy supply, and micro-miniature intelligent wearable energy systems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0007] A method for preparing a structure-tunable flexible nylon 11 piezoelectric separation fiber membrane includes the following steps:

[0008] (1) Nylon 11 particles and inorganic nanofillers were added to a cosolvent system to react and a homogeneous matrix solution A was prepared.

[0009] (2) Nylon 11 particles and polyethylene glycol were added to a co-solvent system to react and prepare a homogeneous matrix solution B.

[0010] (3) The homogeneous matrix solutions A and B are defoamed and then coaxially electrospun to form a film, thus obtaining a flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure.

[0011] Furthermore, Nylon 11 particles are commercially available products, such as RTP Nylon 11 and French Arkema Nylon 11 Besmotl.

[0012] Furthermore, in step (1), the mass ratio of nylon 11 particles to the co-solvent system is 1:1 to 5; the mass ratio of nylon 11 particles to inorganic nanofillers is 1 to 2:0 to 0.5.

[0013] Furthermore, in step (2), the mass ratio of nylon 11 particles, polyethylene glycol, and co-solvent system is 0–2.5:5–20:5–15.

[0014] Furthermore, the co-solvent system comprises an organic protic acid solvent and a benign solvent in a volume ratio of 1:1 to 10.

[0015] Furthermore, the organic protic acid solvent is at least one selected from formic acid, acetic acid, propionic acid, oxalic acid, benzoic acid, malonic acid, trichloroacetic acid, and trifluoroacetic acid;

[0016] The benign solvent is at least one of hexafluoroisopropanol, acetone and dichloromethane.

[0017] Furthermore, the inorganic nanofiller is at least one of barium titanate nanoparticles, zinc oxide nanoparticles, lead zirconate titanate, carbon nanotubes, and graphene nanosheets.

[0018] Furthermore, the reaction temperature in steps (1) and (2) is 25–70°C, and the stirring speed is 200–600 rpm.

[0019] Furthermore, the polyethylene glycol is at least one of PEG300, PEG600 and PEG4000.

[0020] Furthermore, the coaxial electrospinning process in step (3) is as follows:

[0021] The solution injected into A is a homogeneous matrix solution B, and the injection rate is 1.0-2.5 mL / h;

[0022] The solution injected into B is a homogeneous matrix solution A, and the injection rate is 2.0-7.5 mL / h;

[0023] The distance from the needle tip to the roller shaft is 5-15cm;

[0024] The receiver roller rotates at a speed of 30-500 rpm;

[0025] The positive voltage is 12-18V, and the negative voltage is -1.0 to -1.5V.

[0026] Furthermore, the defoaming time is 1–5 minutes.

[0027] Furthermore, after electrospinning, the process also includes vacuum annealing, pure water immersion with ultrasonic displacement, and drying. The vacuum annealing temperature is 40-120℃, the annealing time is 2-6h, the pure water immersion with ultrasonic displacement time is 0.5-2.5h, and the drying method is vacuum drying or freeze drying. The vacuum drying temperature is 40-80℃, and the drying time is 8-24h.

[0028] A flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure was prepared by the above method.

[0029] The above-mentioned flexible nylon 11 piezoelectric separation fiber membrane is used in the preparation of flexible energy harvesting devices and energy storage devices.

[0030] A lithium-ion battery that uses the aforementioned flexible nylon 11 piezoelectric separation fiber membrane as a separator between the positive electrode material and the negative electrode material.

[0031] Furthermore, this lithium-ion battery is a self-charging lithium-ion battery.

[0032] Furthermore, the assembly method of the self-charging lithium-ion battery is as follows: the positive electrode tab, positive electrode sheet, separator, negative electrode sheet, and negative electrode tab are sequentially aligned and wrapped in an aluminum-plastic film, and three sides are heat-sealed, leaving one side to inject electrolyte; then, the preliminarily assembled soft-pack lithium-ion battery is placed in a vacuum oven to dry for a certain period of time, and then transferred to a glove box filled with argon atmosphere to inject a quantitative amount of electrolyte, and then completely sealed using a vacuum heat sealer, finally obtaining a self-charging flexible lithium-ion battery.

[0033] Furthermore, the positive electrode tab is an aluminum tab, the positive electrode material is lithium iron phosphate (LiFePO4), the separator is a flexible hollow nylon 11 piezoelectric fiber membrane, the negative electrode tab is a nickel tab, the negative electrode material is graphite, the vacuum drying temperature is 60℃, the vacuum drying time is 12h, and the injected electrolyte is lithium hexafluorophosphate electrolyte (1M LiPF6 in EC:DMC=1:1 vol%).

[0034] The beneficial effects of this invention are:

[0035] 1. This invention effectively controls the composition, macroscopic morphology, and piezoelectric output performance of piezoelectric fiber membranes by combining co-solvent-induced crystallization, coaxial electrospinning, and in-situ pore formation. The piezoelectric fiber membranes prepared by this invention can effectively control the fiber size by adjusting the concentration of the spinning solution, increase the piezoelectric active phase composition by inducing the formation of the polar crystalline phase (δ' phase) in nylon 11 through co-solvent, and control the piezoelectric output capability by adjusting the axial distance between the needle and the roller and the rotation speed of the roller, thereby improving the tightness of the fiber overlap and significantly enhancing the electromechanical output performance of the piezoelectric fiber membrane.

[0036] 2. The present invention can effectively adjust the structural morphology of the flexible nylon 11 piezoelectric separation fiber membrane by adjusting the concentration of the solvent on the AB axis, the distance between the needle and the roller, the rotation speed of the roller, and the magnitude of the electric field voltage. For example, it can be a solid structure, a porous structure, a hollow structure, a network interwoven structure, a dendritic structure, and a covered structure, thereby adjusting its piezoelectric output performance.

[0037] 3. The spinning solution in this invention is a co-solvent system that can induce the formation of high-voltage electroactive phase nylon 11. Furthermore, the electrospinning and co-solvent system synergistically enhance the induction and control of suitable metastable crystalline phases (high-voltage electroactive crystalline phases), such as piezoelectric γ phase or ferroelectric δ′ phase, thereby improving the piezoelectric output capability of nylon 11 fibers and enabling the obtained nylon 11 fibers to have a synergistic effect of high-voltage output and strong flexibility.

[0038] 4. The piezoelectric fiber membrane prepared by this invention can be used as a separator for batteries and has the advantages of not being swollen by electrolyte and being flexible and strong. It can be used to prepare flexible self-charging batteries, such as self-charging lithium-ion batteries, thus giving it great potential application prospects in energy storage devices, emergency energy supply and micro-miniature smart wearable energy systems. Attached Figure Description

[0039] Figure 1 This is a piezoelectric test image of the flexible hollow piezoelectric fiber membrane prepared according to an embodiment of the present invention;

[0040] Figure 2 This is a SEM image of the porous nylon 11 piezoelectric fiber membrane prepared in Example 1 of the present invention.

[0041] Figure 3 The piezoelectric voltage and current output performance of the porous nylon 11 piezoelectric fiber membrane prepared in Example 1 of this invention are shown in the figure.

[0042] Figure 4 A battery charge / discharge performance diagram of the porous nylon 11 piezoelectric fiber membrane prepared in Example 1 of this invention, used as a separator in a lithium-ion battery;

[0043] Figure 5A battery self-charging performance diagram of the porous nylon 11 piezoelectric fiber membrane prepared in Example 1 of the present invention as a separator for lithium-ion batteries;

[0044] Figure 6 The images show the surface and cross-sectional SEM morphology of the flexible hollow nylon 11 piezoelectric fiber membrane prepared in Example 2 of this invention.

[0045] Figure 7 The diagram shows the piezoelectric voltage and current output performance of the flexible hollow nylon 11 piezoelectric fiber membrane prepared in Example 2 of this invention.

[0046] Figure 8 This is a photograph of a lithium-ion battery assembled using the flexible hollow nylon 11 piezoelectric fiber membrane as a separator in Embodiment 2 of the present invention.

[0047] Figure 9 The diagram shows the charge-discharge performance of a commercially available polyolefin (PP) separator used as a separator in a lithium-ion battery in the comparative example of this invention.

[0048] Figure 10 This is a battery charge / discharge performance diagram of the flexible hollow nylon 11 piezoelectric fiber membrane used as a separator in lithium-ion batteries in Embodiment 2 of the present invention;

[0049] Figure 11 This is a diagram showing the self-charging performance of a lithium-ion battery based on a flexible hollow nylon 11 piezoelectric fiber membrane in Embodiment 2 of the present invention.

[0050] Figure 12 The images show the surface and cross-sectional SEM images of the flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane prepared in Example 3 of this invention.

[0051] Figure 13 The diagram shows the piezoelectric voltage and current output performance of the flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane prepared in Example 3 of this invention.

[0052] Figure 14 The diagram shows the battery charge-discharge performance of the flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane prepared in Example 3 of the present invention as a separator for lithium-ion batteries.

[0053] Figure 15 The diagram shows the battery self-charging performance of the flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane prepared in Example 3 of the present invention as a separator for lithium-ion batteries.

[0054] Figure 16 The images show the surface and cross-section SEM images of the flexible solid nylon 11 piezoelectric fiber membrane prepared in Example 4 of this invention.

[0055] Figure 17This is a surface SEM image of the flexible network interwoven nylon 11 piezoelectric fiber membrane prepared in Example 5 of the present invention;

[0056] Figure 18 This is a surface SEM image of the flexible dendritic nylon 11 piezoelectric fiber membrane prepared in Example 6 of the present invention;

[0057] Figure 19 This is a cross-sectional SEM image of the flexible core-shell nylon 11 piezoelectric fiber membrane prepared in Example 7 of the present invention. Detailed Implementation

[0058] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0059] Example 1

[0060] A method for preparing a flexible porous high-voltage output nylon 11 piezoelectric fiber membrane includes the following steps:

[0061] (1) Add 2g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% homogeneous nylon 11 solution A.

[0062] (2) Add 1g of nylon 11 particles to 5mL of PEG600 solution and 5mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react at 60℃ with a stirring speed of 400rpm for 6h to obtain 10wt% homogeneous PEG600 / nylon 11 solution B.

[0063] (3) Defoam the homogenized solutions A and B from steps (1) and (2) in a high-speed mixer for 2 minutes;

[0064] (4) Spin 6 mL of the above 20 wt% nylon 11 solution A and 3 mL of the above 10 wt% PEG600 / nylon 11 solution B into a film according to the following spinning procedure: use a coaxial needle of model 18G / 21G, inject the solution in A as 10 wt% PEG600 / nylon 11 solution B, inject the solution in B as 20 wt% nylon 11 solution A, inject A at a rate of 1.0 mL / h, inject B at a rate of 2.0 mL / h, the distance from the needle to the roller is 10 cm, the rotation speed of the receiver roller is 100 rpm, the positive voltage is 14.0 kV, and the negative voltage is -1.1 kV.

[0065] (5) The above coaxial spun membrane was subjected to vacuum annealing, pure water immersion ultrasonic replacement and drying treatment in sequence. The vacuum annealing temperature was 60℃, the pure water immersion ultrasonic treatment was performed for 30 min and the freeze drying was performed for 24 h to obtain a flexible porous nylon 11 piezoelectric fiber membrane.

[0066] Example 2

[0067] A method for preparing a self-charging lithium-ion battery based on a flexible hollow nylon 11 piezoelectric separation membrane includes the following steps:

[0068] (1) Add 2g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% homogeneous nylon 11 solution A.

[0069] (2) Add 5 mL of PEG4000 solution to 5 mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react at 60 °C with a stirring speed of 400 rpm for 2 h to obtain 50 wt% homogeneous PEG4000 solution B.

[0070] (3) Defoam the homogenized solutions A and B from steps (1) and (2) in a high-speed mixer for 2 minutes;

[0071] (4) Spin 6 mL of the above 20 wt% Nylon 11 solution A and 3 mL of the above 50 wt% PEG4000 solution B into a film according to the following spinning procedure: use a coaxial needle of model 18G / 21G, inject the solution in A as 50 wt% PEG4000 solution B, inject the solution in B as 20 wt% Nylon 11 solution A, inject the rate of A as 1.0 mL / h, inject the rate of B as 2.0 mL / h, the distance from the needle to the roller is 8 cm, the rotation speed of the receiver roller is 200 rpm, the positive voltage is 14.5 kV, and the negative voltage is -1.2 kV.

[0072] (5) The above coaxial spun membrane was subjected to vacuum annealing, pure water immersion ultrasonic replacement and drying treatment in sequence. The vacuum annealing temperature was 60℃, the pure water immersion ultrasonic treatment was 1h and the freeze drying was 24h to obtain a flexible hollow nylon 11 piezoelectric fiber membrane.

[0073] (6) The flexible hollow nylon 11 piezoelectric fiber membrane obtained above is used as the separator of lithium-ion battery. It is sandwiched between the positive and negative electrode materials and connected to the positive and negative electrode tabs and encapsulated in aluminum-plastic film. The flexible lithium-ion battery is prepared by encapsulation, drying, liquid injection and formation. The battery performance is tested after standing for 24 hours.

[0074] The flexible hollow nylon 11 piezoelectric fiber membrane was cut into pieces measuring 2.5 × 2.5 cm.2 Square samples were prepared and encapsulated with commercial copper tape and polyimide film to form a shape like... Figure 1 The piezoelectric device shown is used for piezoelectric performance testing.

[0075] Example 3

[0076] A method for preparing a flexible hollow nylon 11 / barium titanate composite piezoelectric separation membrane includes the following steps:

[0077] (1) Add 2g of nylon 11 particles and 0.4g of barium titanate powder (BTO) to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% nylon 11 / BTO blend solution A.

[0078] (2) Add 5 mL of PEG4000 solution to 5 mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react at 60 °C with a stirring speed of 400 rpm for 2 h to obtain 50 wt% homogeneous PEG4000 solution B.

[0079] (3) Defoam the homogenized solutions A and B from steps (1) and (2) in a high-speed mixer for 2 minutes;

[0080] (4) Spin 6 mL of the above 20 wt% Nylon 11 / BTO blend solution A and 3 mL of the above 50 wt% PEG4000 solution B into a film according to the following spinning procedure: use a coaxial needle of model 18G / 21G, inject the solution in A as 50 wt% PEG4000 solution B, inject the solution in B as 20 wt% Nylon 11 solution A, inject A at a rate of 1.0 mL / h, inject B at a rate of 2.0 mL / h, the distance from the needle to the roller is 8 cm, the rotation speed of the receiver roller is 200 rpm, the positive voltage is 16 kV, and the negative voltage is -1.1 kV.

[0081] (5) The above coaxial spun membrane was subjected to vacuum annealing, pure water immersion ultrasonic replacement and drying treatment in sequence. The vacuum annealing temperature was 60℃, the pure water immersion ultrasonic treatment was performed for 1 hour and the freeze drying was performed for 24 hours to obtain a flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane.

[0082] Example 4

[0083] A method for preparing a flexible solid nylon 11 piezoelectric separation membrane includes the following steps:

[0084] (1) Add 2g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% homogeneous nylon 11 solution.

[0085] (2) Defoam the homogenized solution in step (1) in a high-speed mixer for 2 minutes;

[0086] (3) Spin 6 mL of the above 20 wt% nylon 11 homogeneous solution into a film according to the following spinning procedure: use needle type 21G, the solution in A is 20 wt% homogeneous nylon 11 solution, the injection rate of A is 1.0 mL / h, the distance between the needle and the roller is 15 cm, the rotation speed of the receiver roller is 200 rpm, the positive voltage is 8 kV, and the negative voltage is -1.1 kV.

[0087] (5) The above-mentioned spun film was subjected to vacuum annealing and drying treatment in sequence. The vacuum annealing temperature was 60℃ and the drying time was 24h to obtain a flexible solid nylon 11 piezoelectric fiber film.

[0088] Example 5

[0089] A method for preparing a flexible, interwoven nylon 11 piezoelectric separation membrane includes the following steps:

[0090] (1) Add 2g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% homogeneous nylon 11 solution.

[0091] (2) Defoam the homogenized solution in step (1) in a high-speed mixer for 2 minutes;

[0092] (3) Spin 6 mL of the above 20 wt% nylon 11 homogeneous solution into a film according to the following spinning procedure: use needle type 21G, the solution in A is 20 wt% homogeneous nylon 11 solution, the injection rate of A is 2.0 mL / h, the distance between the needle and the roller is 10 cm, the rotation speed of the receiver roller is 30 rpm, the positive voltage is 8 kV, and the negative voltage is -1.1 kV.

[0093] (5) The above-mentioned spun membrane was subjected to vacuum annealing and drying treatment in sequence. The vacuum annealing temperature was 60℃ and the drying time was 24h to obtain a flexible network interwoven nylon 11 piezoelectric fiber membrane.

[0094] Example 6

[0095] A method for preparing a flexible dendritic nylon 11 piezoelectric separation membrane includes the following steps:

[0096] (1) Add 1g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 10wt% homogeneous nylon 11 solution.

[0097] (2) Defoam the homogenized solution in step (1) in a high-speed mixer for 2 minutes;

[0098] (3) Spin 6 mL of the above 10 wt% homogeneous nylon 11 solution into a film according to the following spinning procedure: use needle type 21G, inject solution A is 10 wt% homogeneous nylon 11 solution, inject A rate is 0.5 mL / h, the distance between the needle and the roller is 8 cm, the rotation speed of the receiver roller is 30 rpm, the positive voltage is 8.5 kV, and the negative voltage is -1.1 kV.

[0099] (5) The above-mentioned spun membrane was subjected to vacuum annealing and drying treatment in sequence. The vacuum annealing temperature was 60℃ and the drying time was 24h to obtain a flexible dendritic nylon 11 piezoelectric fiber membrane.

[0100] Example 7

[0101] A method for preparing a flexible core-shell structured nylon 11 piezoelectric fiber membrane includes the following steps:

[0102] (1) Add 2g of nylon 11 particles to 10mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9, and react and dissolve at 60℃ with a stirring speed of 400rpm for 6h to obtain a 20wt% homogeneous nylon 11 solution A.

[0103] (2) 1 g of nylon 11 particles were placed in 10 mL of trifluoroacetic acid solvent and hexafluoroisopropanol solvent with a volume ratio of 1:9 and reacted at 60 °C with a stirring speed of 400 rpm for 6 h to obtain a homogeneous nylon 11 solution B of 10 wt%.

[0104] (3) Defoam the homogenized solutions A and B from steps (1) and (2) in a high-speed mixer for 2 minutes;

[0105] (4) Spin 6 mL of the above 20 wt% nylon 11 solution A and 3 mL of the above 10 wt% nylon 11 solution B into a film according to the following spinning procedure: use a coaxial needle of model 18G / 21G, push the solution in A to be 10 wt% nylon 11 solution B, push the solution in B to be 20 wt% nylon 11 solution A, push the rate of A to be 1.0 mL / h, push the rate of B to be 2.0 mL / h, the distance from the needle to the roller is 12 cm, the rotation speed of the receiver roller is 100 rpm, the positive voltage is 14.0 kV, and the negative voltage is -1.1 kV.

[0106] (5) The above coaxial spun membrane was subjected to vacuum annealing and drying treatment in sequence. The vacuum annealing temperature was 60℃ and the drying time was 24h to obtain a flexible core-shell nylon 11 piezoelectric fiber membrane.

[0107] Comparative Example

[0108] This comparative example provides a method for preparing a lithium-ion battery based on a commercially available polyolefin (PP) separator membrane, comprising the following steps:

[0109] (1) The assembly method of lithium-ion battery is to sequentially align and wrap the positive electrode tab, positive electrode sheet, commercial polyolefin PP separator, negative electrode sheet, and negative electrode tab in an aluminum-plastic film, heat seal three sides, and leave one side to inject electrolyte.

[0110] (2) The preliminarily assembled soft-pack lithium-ion batteries were dried in a vacuum oven at 60°C for 12 hours;

[0111] (3) Then, 1 mL of lithium hexafluorophosphate electrolyte (1M LiPF6 in EC:DMC = 1:1 vol%) was injected into a glove box filled with argon atmosphere, and it was completely sealed using a vacuum heat sealer to finally obtain a commercial flexible lithium-ion battery.

[0112] Experimental testing

[0113] 1. Performance testing of flexible nylon 11 piezoelectric fiber membrane

[0114] The composition, macro / micro morphology, and piezoelectric output performance of piezoelectric fiber membranes were effectively controlled by combining co-solvent-induced crystallization, coaxial electrospinning, and in-situ pore formation. The flexible piezoelectric fiber membranes in the examples were prepared and assembled as shown in the figure. Figure 1 The piezoelectric nanogenerator shown. The morphology and piezoelectric properties of the piezoelectric fibers prepared in Examples 1 and 2 were observed, as well as tested. Figure 2 , Figure 3 , Figure 6 and Figure 7 As shown.

[0115] Depend on Figure 2 and Figure 6 As can be seen, the nylon 11 piezoelectric fibers prepared by this invention exhibit a porous and hollow tubular shape, with a filament diameter of approximately 2.0-2.5 μm. Furthermore, the porous fibers have uniform spacing and regular morphology, which is beneficial for stress concentration to generate greater piezoelectric output. Further testing was conducted on the piezoelectric output voltage and current.

[0116] like Figure 3 and Figure 7 The test results show that the piezoelectric output voltage and current of the flexible porous nylon 11 piezoelectric fiber membrane prepared by the present invention are 12.5V and 470nA, respectively, while the piezoelectric output voltage and current of the flexible hollow nylon 11 piezoelectric fiber membrane are 18.5V and 1.2μA, respectively. The piezoelectric performance is greatly improved, indicating that structural optimization can improve the piezoelectric output performance of the material.

[0117] Furthermore, porous nylon 11 fiber membranes were used as separators in the assembly of pouch cells. The charge / discharge performance of the pouch cells is shown in the figure below. Figure 4 As shown, the piezoelectric separator in this invention can be used as a substitute for commercial polyolefin (PP) separators.

[0118] Finally, the self-charging performance of the pouch battery was tested, such as... Figure 5 As shown, by continuous tapping (at a frequency of 1.7Hz, using a force of 9N for 90s), the battery can be charged from 0.8V to 1.029V, successfully charging 229mV. Discharging to 0.8V with a constant current of 0.05mA can be sustained for 20s, with a charging capacity of 0.28μAh. The above results fully demonstrate that the piezoelectric separator in this invention has good self-charging performance as a separator for lithium-ion batteries.

[0119] 2. Battery performance assembled with flexible hollow nylon 11 piezoelectric fiber membrane

[0120] Hollow nylon 11 fiber membranes were used as separators in the assembly of soft-pack batteries. A photograph of the actual product is shown below. Figure 8 As shown in the figure, the charge-discharge performance of a soft-pack battery using a flexible hollow nylon 11 piezoelectric fiber membrane as the separator for a lithium-ion battery is compared with that of a commercial polyolefin (PP) separator. Figure 9 and Figure 10 As shown.

[0121] Depend on Figure 9 and Figure 10 It can be seen that the flexible hollow nylon 11 piezoelectric fiber membrane used as the separator for lithium-ion batteries has similar charge and discharge performance to commercial polyolefin PP separators. Furthermore, the piezoelectric separator in this invention has a lower leakage voltage (0.7V) than the commercial polyolefin PP separator (1.0V), indicating that the piezoelectric separator in this invention can be used as a substitute for the commercial polyolefin PP separator.

[0122] Finally, the self-charging performance of the pouch battery under this structure was tested. Figure 11 It can be seen that at a frequency of 1.7Hz, when continuously struck with a force of 9N for 600s, the battery can be charged from 0.8V to 1.015V, successfully charging 215mV. When discharged to 0.8V with a constant current of 0.05mA for 35.5s, the charging capacity reaches 0.4931μAh. The above results fully demonstrate that the piezoelectric separator in this invention has good self-charging performance as a separator for lithium-ion batteries.

[0123] 3. Morphology of flexible hollow nylon 11 / BTO composite piezoelectric fiber membrane and performance of assembled batteries

[0124] The morphology of the piezoelectric fibers prepared in Example 3 was observed and their piezoelectric properties were tested, such as... Figure 12 and Figure 13 As shown. From Figure 12 As can be seen, the nylon 11 / BTO composite piezoelectric fiber membrane exhibits a hollow tubular shape and is loaded with BTO nanoparticles, indicating that the hollow nylon 11 / BTO composite piezoelectric fiber membrane can be prepared by the method of the present invention. Figure 13 It can be seen that the piezoelectric output voltage of the hollow nylon 11 / BTO composite piezoelectric fiber membrane is 33V and 1.25μA, which is significantly improved, indicating that structural optimization and composite piezoelectric filler can improve the piezoelectric output performance of the material.

[0125] Furthermore, a hollow nylon 11 / BTO composite piezoelectric fiber membrane was used as the separator for assembling a pouch cell. The charge / discharge performance of this pouch cell is shown in the figure below. Figure 14 As shown. By Figure 14 It can be seen that the flexible hollow nylon 11 piezoelectric fiber membrane used as the separator for lithium-ion batteries has similar charge and discharge performance to commercial polyolefin PP separators. Furthermore, the piezoelectric separator in this invention has a lower leakage voltage (0.7V) than the commercial polyolefin PP separator (1.0V), indicating that the piezoelectric separator in this invention can be used as a substitute for the commercial polyolefin PP separator.

[0126] Finally, the self-charging performance of the pouch battery with this structure was tested. At a frequency of 1.7Hz, after being continuously struck with a force of 9N for 600 seconds, the battery could charge from 0.8V to 1.02V, successfully charging to 220mV. Discharging to 0.8V with a constant current of 5μA lasted for 3216 seconds, achieving a charging capacity of 4.47μAh. Figure 15 The above results fully demonstrate that the piezoelectric separator in this invention has excellent self-charging performance as a separator for lithium-ion batteries.

[0127] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a structurally adjustable flexible nylon 11 piezoelectric separation fiber membrane, characterized in that, Includes the following steps: (1) Nylon 11 particles and inorganic nanofillers are added to a cosolvent system to react and prepare a homogeneous matrix solution A; wherein the mass ratio of nylon 11 particles to inorganic nanofillers is 1~2:0~0.5; the cosolvent system includes an organic protic acid solvent and a benign solvent with a volume ratio of 1:1~10. The organic protic acid solvent is at least one selected from formic acid, acetic acid, propionic acid, oxalic acid, benzoic acid, malonic acid, trichloroacetic acid, and trifluoroacetic acid; the benign solvent is at least one selected from hexafluoroisopropanol, acetone, and dichloromethane. (2) Nylon 11 particles and polyethylene glycol are added to a co-solvent system to react and prepare a homogeneous matrix solution B; wherein the mass ratio of nylon 11 particles, polyethylene glycol and co-solvent system is 0~2.5:5~20:5~15; (3) Defoaming treatment was performed on homogeneous matrix solutions A and B, and then coaxial electrospinning was used to form a film to obtain a flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass ratio of nylon 11 particles to the co-solvent system is 1:1~5.

3. The preparation method according to claim 1, characterized in that, The inorganic nanofiller is at least one of the following: barium titanate nanoparticles, zinc oxide nanoparticles, lead zirconate titanate, carbon nanotubes, and graphene nanosheets.

4. The preparation method according to claim 1, characterized in that, The reaction temperature in steps (1) and (2) is 25~70 ℃ and the stirring speed is 200~600 rpm.

5. The preparation method according to claim 1, characterized in that, The coaxial electrospinning process in step (3) is as follows: The solution injected into A is a homogeneous matrix solution B, and the injection rate is 1.0-2.5 mL / h; The solution injected into B is a homogeneous matrix solution A, and the injection rate is 2.0-7.5 mL / h; The distance from the needle tip to the roller shaft is 5-15 cm; The receiver roller rotates at a speed of 30-500 rpm; The positive voltage is 12-18 V, and the negative voltage is -1.0 to -1.5 V.

6. A flexible nylon 11 piezoelectric separation fiber membrane with adjustable structure, characterized in that, It is prepared by the method described in any one of claims 1 to 5.

7. The application of the flexible nylon 11 piezoelectric separation fiber membrane according to claim 6 in the preparation of flexible energy harvesting devices and energy storage devices.

8. A lithium-ion battery, characterized in that, The lithium-ion battery uses the flexible nylon 11 piezoelectric separation fiber membrane as described in claim 6 as the separator between the positive electrode material and the negative electrode material.

Images