GeP nanoparticle-PVDF composite piezoelectric film and preparation method and application thereof

Abstract

The invention discloses a GeP nanoparticle-PVDF composite piezoelectric film and a preparation method and application thereof.The method comprises the steps that firstly, grinding pretreatment is conducted on bulk-phase GeP, and then GeP nanoparticle dispersion liquid is prepared through a liquid-phase stripping method; then concentrating and collecting the GeP nano particles through rotary evaporation; adding the concentrated GeP nano particle dispersion liquid into a PVDF (Polyvinylidene Fluoride) solution to obtain a GeP nano particle-PVDF composite dispersion liquid; and finally, carrying out electrostatic spinning by utilizing the GeP nano particle-PVDF composite dispersion liquid to prepare the GeP nano particle-PVDF composite piezoelectric film for the lithium metal battery. According to the method, GeP nanoparticles and PVDF are compounded, generation of a beta phase in PVDF is effectively induced, piezoelectric output of the composite piezoelectric film is improved, uniform deposition and stripping of lithium metal are promoted, growth of lithium dendrites is inhibited, the cycle life of a lithium metal battery is prolonged, and the safety performance of the lithium metal battery is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of PVDF composite piezoelectric thin films, and relates to a GeP nanoparticle-PVDF composite piezoelectric thin film, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the rapid development of society and the increase in population, fossil energy has gradually dried up, and the ecological environment has deteriorated day by day. Developing clean energy and protecting green environmental resources have become two major problems faced by current society. Energy storage and conversion are the two most important technologies in today's green energy and renewable energy. Among various electrochemical energy storage devices, lithium metal batteries have attracted the attention of many researchers due to their higher energy density and excellent cycle life. However, there are still some problems in the development of high specific energy lithium anodes. For example, uncontrollable dendrite growth during lithium deposition will not only lead to capacity loss, but also cause internal short circuits in the battery, resulting in potential safety hazards. The unique piezoelectric effect of piezoelectric thin films can effectively address such problems. Specifically, when a piezoelectric thin film is squeezed during the nucleation and growth of lithium dendrites, a piezoelectric electric field will be generated, thereby regulating the deposition of lithium ions and eliminating lithium buds. Polyvinylidene fluoride (PVDF) has unique piezoelectric properties, and at the same time has the advantages of light weight, softness, and easy processing. It is one of the most widely used piezoelectric materials at present and is very suitable for use as a separator for lithium metal batteries.

[0003] The piezoelectricity of PVDF is mainly due to the presence of the β-polar crystalline form in it. Compared with the α-phase (TGTG) conformation in which the dipoles arranged antiparallel to the carbon chain cancel each other out, the all-trans chain conformation (TTT) in the β-phase exhibits the largest dipole moment, can form a strong macroscopic polarization, and has strong piezoelectricity. However, the piezoelectric output of conventional PVDF is relatively low. To obtain more piezoelectric properties, more molecular chains of the β-phase need to be generated and aligned in a specific direction to produce a macroscopic piezoelectric effect. Guang et al. prepared porous PVDF piezoelectric thin films by the nanoparticle template method and voltage polarization. The piezoelectric thin film exhibited a piezoelectric output voltage of about 1V. Although the above scheme can effectively prepare piezoelectric thin films, its output voltage is limited, and it cannot effectively inhibit the growth of lithium dendrites, affecting the cycle life and safety performance of lithium metal batteries. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the present invention provides a GeP nanoparticle-PVDF composite piezoelectric thin film, a preparation method thereof, and an application thereof, so as to solve the technical problem that the output voltage of the PVDF piezoelectric thin film in the prior art is limited and it cannot effectively inhibit the growth of lithium dendrites.

[0005] The present invention is realized through the following technical solutions:

[0006] A preparation method of GeP nanoparticle-PVDF composite piezoelectric thin film, comprising the following steps:

[0007] S1: Grind and pre-treat bulk GeP, and then prepare a GeP nanoparticle dispersion by liquid-phase exfoliation method; then concentrate and collect the GeP nanoparticles by rotary evaporation.

[0008] S2: Add the concentrated GeP nanoparticle dispersion to the PVDF solution and stir evenly to obtain a GeP nanoparticle-PVDF composite dispersion;

[0009] S3: Electrospinning is carried out using the GeP nanoparticle-PVDF composite dispersion to obtain the GeP nanoparticle-PVDF composite piezoelectric thin film.

[0010] Preferably, in step S1, during the grinding pre-treatment process, the grinding time is 0.8-1.5 h.

[0011] Preferably, in step S1, during the liquid-phase exfoliation process, specifically: first, use an ultrasonic cleaner to treat the DMF suspension of GeP, then continue ultrasonic exfoliation using an ultrasonic cell disruptor, and finally perform centrifugation to obtain the GeP nanoparticle dispersion.

[0012] Preferably, use an ultrasonic cleaner to treat the DMF suspension of GeP, then continue ultrasonic exfoliation using an ultrasonic cell disruptor, and finally perform centrifugation to obtain the GeP nanoparticle dispersion, specifically: first, use an ultrasonic cleaner to ultrasonically treat the DMF suspension of GeP at a power of 250-400 W for 2-3 h, then use an ultrasonic cell disruptor to perform ultrasonic exfoliation treatment at a power of 400-600 W for 2-5 h, and finally perform centrifugation treatment; during the centrifugation treatment process, first centrifuge at a rotation speed of 2000-3000 rpm for 30 min, take the supernatant, and then centrifuge the supernatant at a rotation speed of 8000-10000 rpm for 30 min to obtain the GeP nanoparticle dispersion.

[0013] Preferably, in step S1, during the rotary evaporation process, the temperature is 70-90 °C and the rotation speed is 100-150 rpm.

[0014] Preferably, in step S2, the preparation process of the GeP nanoparticle-PVDF composite dispersion is: add the concentrated GeP nanoparticle dispersion and PVDF to a mixed solution of N,N-dimethylformamide and acetone, and stir until the PVDF is completely dissolved and the GeP nanoparticles are evenly dispersed to obtain the GeP nanoparticle-PVDF composite dispersion.

[0015] Preferably, the mass fraction of PVDF in the GeP nanoparticle-PVDF composite dispersion is 10% to 15%, and the GeP nanoparticles account for 1% to 3% of the solid mass in the GeP nanoparticle-PVDF composite dispersion.

[0016] Preferably, in step S3, during the electrospinning process, the electric field strength is 10 to 15 kV.

[0017] A GeP nanoparticle-PVDF composite piezoelectric film is prepared by the above method.

[0018] The application of the above GeP nanoparticle-PVDF composite piezoelectric film in a lithium metal battery uses the above GeP nanoparticle-PVDF composite piezoelectric film as a battery separator; the piezoelectric output voltage of the piezoelectric device assembled with the composite film is 2.9 to 4.5 V.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The present invention provides a preparation method of a GeP nanoparticle-PVDF composite piezoelectric film for a lithium metal battery. First, as a heterogeneous nucleating agent, GeP nanoparticles promote the formation of a β-phase with an all-trans (TTT) conformation of PVDF molecular chains through surface energy differences, significantly enhancing the piezoelectric response. Experimental data shows that the piezoelectric output of the PVDF film added with GeP is significantly improved. In addition, the polar groups on the surface of GeP nanoparticles form hydrogen bonds or dipole interactions with the C-F bonds of PVDF, further stabilizing the β-phase structure; second, the semiconductor characteristics of GeP provide a conductive channel for PVDF, enabling the rapid migration of charges generated by piezoelectricity and avoiding local charge accumulation, thereby enhancing the effective output voltage. The conductive network formed by GeP nanoparticles can homogenize the interfacial electric field of lithium ion deposition and inhibit the high current density at the tip of dendrites; third, the nanofibers formed by electrospinning effectively increase the porosity of the film, promote the infiltration of the electrolyte and the uniform diffusion of lithium ions, and reduce local polarization. During the electrospinning process, the PVDF molecular chains are oriented under the action of an electric field and tensile stress, and the proportion of the β-phase further increases. When the growth of lithium dendrites applies pressure to the film, the piezoelectric effect of PVDF generates a reverse electric field, offsetting the local electrochemical potential gradient and inhibiting the enrichment of lithium ions at the tip of dendrites. In summary, this method combines GeP nanoparticles with PVDF to form a porous piezoelectric film with a nanofibrous structure through electrospinning technology, realizing the simple and low-cost preparation of a high piezoelectric output PVDF-based flexible film, thus making it possible for the PVDF-based composite film to be widely used in lithium metal battery separators.

[0021] Further, in step S1, during the grinding pretreatment process, the grinding time is 0.8 to 1.5 h, and small-sized bulk GeP can be obtained, which is beneficial for subsequent liquid-phase exfoliation.

[0022] Furthermore, in step S1, the GeP nanoparticle dispersion is prepared by a liquid-phase exfoliation method, specifically as follows: First, use an ultrasonic cleaner to ultrasonically treat the DMF suspension of GeP at a power of 250 - 400 W for 2 - 3 h, then use an ultrasonic cell disruptor to perform ultrasonic exfoliation treatment at a power of 400 - 600 W for 2 - 5 h, and finally perform centrifugation. During the centrifugation process, first centrifuge at a speed of 2000 - 3000 rpm for 30 min, take the supernatant, and then centrifuge the supernatant at a speed of 8000 - 10000 rpm for 30 min to obtain the GeP nanoparticle dispersion. The GeP nanoparticles prepared under these process parameters have a particle size of about 68 nm and are evenly dispersed. Nanomaterials with this particle size help induce the formation of the β-phase in PVDF, and the resulting composite piezoelectric film has good piezoelectric output performance.

[0023] Furthermore, in step S1, during the rotary evaporation process, the temperature is 70 - 90 °C, the rotation speed is 100 - 150 rpm, and the concentration of GeP nanoparticles in the concentrated dispersion is 2 mg / mL -1 , which is beneficial for subsequent electrospinning.

[0024] Furthermore, in step S2, the preparation process of the GeP nanoparticle - PVDF composite dispersion is as follows: Add the concentrated GeP nanoparticle dispersion and PVDF to a mixed solution of N,N-dimethylformamide and acetone, and stir until PVDF is completely dissolved and GeP nanoparticles are evenly dispersed to obtain the GeP nanoparticle - PVDF composite dispersion. When using DMF / acetone as the solvent to prepare the composite dispersion, the fibers spun by electrospinning are finer, smoother, and have a more uniform diameter distribution.

[0025] Furthermore, the mass fraction of PVDF in the GeP nanoparticle - PVDF composite dispersion is 10% - 15%, and GeP nanoparticles account for 1% - 3% of the solid mass in the GeP nanoparticle - PVDF composite dispersion. At this concentration, the composite dispersion can smoothly undergo electrospinning.

[0026] Furthermore, in step S3, during the electrospinning process, the electric field strength is 10 - 15 kV, which can make the fibers of the spun film have uniform thickness and no beading, and the electrospinning effect and the performance of the film are more excellent. Description of the Drawings

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other relevant drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic flowchart of the preparation method of GeP nanoparticle - PVDF composite piezoelectric film in the present invention;

[0029] Figure 2 It is the particle size distribution diagram of GeP nanoparticles in the present invention;

[0030] Figure 3 It is the SEM image of the piezoelectric films prepared in Comparative Example 1 and Examples 1 - 3 in the present invention;

[0031] Figure 4 It is the FTIR spectrum of the piezoelectric films prepared in Comparative Example 1 and Examples 1 - 3 in the present invention;

[0032] Figure 5 It is the test result of piezoelectric voltage output of the piezoelectric films prepared in Comparative Example 1 and Examples 1 - 3 in the present invention;

[0033] Figure 6 It is the test result of piezoelectric current output of the piezoelectric films prepared in Comparative Example 1 and Examples 1 - 3 in the present invention;

[0034] Figure 7 It is the time - voltage test result of the lithium - metal symmetric battery prepared with the separator materials of Comparative Examples 1 - 2 and Example 3 in the present invention;

[0035] Figure 8 It is the cycle performance test result of the lithium - metal battery prepared with the separator materials of Comparative Examples 1 - 2 and Example 3 in the present invention. Specific Embodiments

[0036] To enable those skilled in the art to understand the features and effects of the present invention, the following will generally explain and define the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used herein shall have the ordinary meaning understood by those skilled in the art regarding the present invention. In case of conflict, the definition in this specification shall prevail.

[0037] The theories or mechanisms described and disclosed herein, whether correct or incorrect, shall not in any way limit the scope of the present invention, that is, the content of the present invention can be implemented without being limited by any specific theory or mechanism.

[0038] In this text, all features defined in the form of numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are only for the sake of brevity and convenience. Accordingly, the description of a numerical range or percentage range should be regarded as having covered and specifically disclosed all possible sub-ranges and individual numerical values (including integers and fractions) within the range.

[0039] In this text, unless otherwise specified, terms such as "comprising", "including", "containing", "having", or similar terms cover the meanings of "consisting of" and "consisting essentially of". For example, "A comprises a" covers the meanings of "A comprises a and others" and "A consists only of a".

[0040] In this text, for the sake of concise description, all possible combinations of all technical features in each embodiment or example are not described. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each embodiment or example can be combined arbitrarily, and all possible combinations should be considered as within the scope described in this specification.

[0041] As Figure 1 shown, the present invention provides a method for preparing a GeP nanoparticle-PVDF composite piezoelectric film for a lithium metal battery, comprising the following steps:

[0042] S1: Grind and pre-treat bulk GeP, and then prepare a GeP nanoparticle dispersion by liquid-phase exfoliation; then concentrate and collect the GeP nanoparticles by rotary evaporation;

[0043] Specifically: Weigh a certain mass of GeP sample into a mortar and grind it for 0.8 - 1.5 h, preferably 1 h. After grinding, add DMF solvent to obtain a 1 mg / mL -1 total of 200 mL GeP-DMF suspension. Use an ultrasonic cleaner to ultrasonically treat the GeP-DMF suspension at a power of 250 - 400 W for 2 h, preferably at a power of 300 W. Then use an ultrasonic cell disruptor to ultrasonically treat it at a power of 400 - 600 W for 3 h, preferably at a power of 500 W. Finally, perform centrifugation. First, centrifuge at a speed of 2000 - 3000 rpm for 30 min, take the supernatant, and then centrifuge at a speed of 8000 - 10000 rpm for 30 min, take the supernatant, to obtain DMF-exfoliated GeP nanoparticles with a particle size distribution of about 68 nm. Then, through rotary evaporation treatment, at a temperature of 70 - 90 °C and a rotation speed of 100 - 150 rpm, the concentration of GeP nanoparticles in the concentrated dispersion is 2 mg / mL -1 .

[0044] S2: Add the concentrated GeP nanoparticle dispersion to the PVDF solution, stir evenly to obtain a GeP nanoparticle-PVDF composite dispersion.

[0045] Specifically: The concentrated GeP nanoparticle dispersion and PVDF are added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at 45 °C at a speed of 300 rpm for 1 h until PVDF is completely dissolved and the GeP nanoparticles are uniformly dispersed. Among them, the mass fraction of PVDF is 10% - 15%, preferably 12.5%, the mass ratio of N,N-dimethylformamide (DMF) to acetone is 2:1, and the GeP nanoparticles account for 1% - 3% of the solid mass in the GeP nanoparticle-PVDF composite dispersion.

[0046] S3: Electrospinning is carried out using the GeP nanoparticle-PVDF composite dispersion to obtain the GeP nanoparticle-PVDF composite piezoelectric film.

[0047] Specifically: The GeP nanoparticle-PVDF composite dispersion is placed in a 20 mL syringe for electrospinning to obtain a composite film. In this step, the electric field strength of electrospinning is 10 - 15 kV, preferably 12 kV, the distance between the spinning needle and the collector is 10 cm, the injection speed of the syringe is 1.5 mL / h, and the roller rotation speed of the collecting device is 500 rpm. Finally, the GeP nanoparticle-PVDF composite film is peeled off from the release paper and placed in an oven at 40 °C for 3 h to remove the residual solvent, obtaining the GeP nanoparticle-PVDF composite piezoelectric film.

[0048] The following further elaborates the present invention in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0049] Conventional instrument and equipment in the art are used in the following embodiments. For the experimental methods without specific conditions noted in the following embodiments, they are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer. Various raw materials are used in the following embodiments. Unless otherwise stated, commercially available products with conventional specifications in the art are used. In the specification of the present invention and the following embodiments, unless otherwise specified, "%" represents weight percentage, "parts" represents weight parts, and the ratio represents weight ratio.

[0050] Comparative Example 1

[0051] (1) PVDF powder is added to a mixed solution of DMF and acetone (the mass ratio of DMF to acetone is 2:1), and magnetically stirred at 45 °C for 1 h to completely dissolve PVDF, and a PVDF solution with a mass fraction of 12.5% is prepared.

[0052] (2) Place the PVDF solution into a 20 mL syringe, set the electrospinning parameters. The electric field strength for electrospinning is 12 kV, the distance between the spinning needle and the collector is 10 cm, the injection speed of the syringe is 1.5 mL / h, and the roller rotation speed of the collection device is 500 rpm. Perform electrospinning to obtain a PVDF membrane.

[0053] (3) Peel the PVDF membrane off the release paper and place it in an oven at 40 °C for 3 h to remove the residual solvent.

[0054] Comparative Example 2

[0055] This comparative example uses a commercial PP separator material, model Celgard 2500.

[0056] Example 1

[0057] (1) Weigh a certain mass of GeP sample and grind it in a mortar for 1 h. After grinding, add DMF solvent to obtain a 1 mg mL -1 GeP-DMF suspension with a total volume of 200 mL. Use an ultrasonic cleaner (total power 300 W) to ultrasonically treat the GeP-DMF suspension at 100% power for 2 h, and then use an ultrasonic cell disruptor (total power 950 W) to ultrasonically treat it at 52% power for 3 h. Finally, perform centrifugation. First, centrifuge at 3000 rpm for 30 min, take the supernatant, and then centrifuge at 8000 rpm for 30 min, take the supernatant to obtain a DMF-exfoliated GeP nanoparticle dispersion. Then, concentrate and collect the GeP nanoparticles in the dispersion by rotary evaporation treatment.

[0058] (2) Add the concentrated GeP nanoparticle dispersion and PVDF to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stir at 45 °C at a speed of 300 rpm for 1 h until the PVDF is completely dissolved and the GeP nanoparticles are evenly dispersed, to prepare a GeP nanoparticle-PVDF composite dispersion. Among them, the mass fraction of PVDF is 12.5%, the mass ratio of N,N-dimethylformamide (DMF) to acetone is 2:1, and the GeP nanoparticles account for 1% of the solid mass in the composite dispersion.

[0059] (3) Place the GeP nanoparticle-PVDF composite dispersion into a 20 mL syringe, set the electrospinning parameters. The electric field strength for electrospinning is 12 kV, the distance between the spinning needle and the collector is 10 cm, the injection speed of the syringe is 1.5 mL / h, and the roller rotation speed of the collection device is 500 rpm. Perform electrospinning to obtain a composite membrane.

[0060] (4) Peel the GeP nanoparticle-PVDF composite membrane off the release paper and place it in an oven at 40 °C for 3 h to remove the residual solvent.

[0061] Example 2

[0062] (1) Weigh a certain amount of GeP sample and grind it in a mortar for 1 h. After grinding, add DMF solvent to obtain 1 mg mL -1 A total of 200mL of GeP-DMF suspension. Use an ultrasonic cleaner (total power of 300W) to ultrasonicate the GeP-DMF suspension at 100% power for 2h, and then use an ultrasonic cell crusher (total power of 950W) to ultrasonicate at 52% power for 3h. Finally, centrifuge at 3000rpm for 30min, take the supernatant, and then centrifuge at 8000rpm for 30min, take the supernatant, and obtain DMF-stripped GeP nanoparticle dispersion. Then concentrate and collect the GeP nanoparticles in the dispersion by rotary evaporation.

[0063] (2) The concentrated GeP nanoparticle dispersion and PVDF were added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at 45°C at a speed of 300 rpm for 1 hour until PVDF was completely dissolved and the GeP nanoparticles were uniformly dispersed, thereby preparing a GeP nanoparticle-PVDF composite dispersion. The mass fraction of PVDF was 12.5%, the mass ratio of N,N-dimethylformamide (DMF) to acetone was 2:1, and the GeP nanoparticles accounted for 2% of the solid mass in the composite dispersion.

[0064] (3) The GeP nanoparticle-PVDF composite dispersion was placed in a 20 mL syringe, and the electrospinning parameters were set, the electric field strength of the electrospinning was 12 kV, the distance between the spinning needle and the collector was 10 cm, the injection speed of the syringe was 1.5 mL / h, and the drum speed of the collecting device was 500 rpm. Electrospinning was performed to obtain a composite membrane.

[0065] (4) The GeP nanoparticle-PVDF composite film was peeled off from the release paper and placed in a 40°C oven for 3 h to remove the residual solvent.

[0066] Example 3

[0067] (1) Weigh a certain amount of GeP sample and grind it in a mortar for 1 h. After grinding, add DMF solvent to obtain 1 mg mL -1A total of 200 mL of GeP-DMF suspension. The GeP-DMF suspension was ultrasonically treated at 100% power for 2 h using an ultrasonic cleaner (total power of 300 W), and then ultrasonically treated at 52% power for 3 h using an ultrasonic cell disruptor (total power of 950 W). Finally, centrifugation was performed. First, centrifugation was carried out at 3000 rpm for 30 min, the supernatant was taken, and then centrifugation was carried out at 8000 rpm for 30 min, and the supernatant was taken to obtain a DMF-exfoliated GeP nanoparticle dispersion. The GeP nanoparticles in the dispersion were concentrated and collected by rotary evaporation treatment.

[0068] (2) The concentrated GeP nanoparticle dispersion and PVDF were added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at 45 °C at a speed of 300 rpm for 1 h until PVDF was completely dissolved and the GeP nanoparticles were uniformly dispersed to prepare a GeP nanoparticle-PVDF composite dispersion. Among them, the mass fraction of PVDF was 12.5%, the mass ratio of N,N-dimethylformamide (DMF) to acetone was 2:1, and the GeP nanoparticles accounted for 3% of the solid mass in the composite dispersion.

[0069] (3) The GeP nanoparticle-PVDF composite dispersion was placed in a 20 mL syringe, and the electrospinning parameters were set. The electric field strength of electrospinning was 12 kV, the distance between the spinning needle and the collector was 10 cm, the injection speed of the syringe was 1.5 mL / h, and the roller speed of the collection device was 500 rpm. Electrospinning was carried out to obtain a composite membrane.

[0070] (4) The GeP nanoparticle-PVDF composite membrane was peeled off from the release paper and placed in an oven at 40 °C for 3 h to remove the residual solvent.

[0071] Example 4

[0072] A preparation method of a GeP nanoparticle-PVDF composite piezoelectric film for a lithium metal battery, comprising the following steps:

[0073] S1: Weigh a certain mass of GeP sample and grind it in a mortar for 0.8 h. After grinding, add DMF solvent to obtain 1 mg / mL -1A total of 200 mL of GeP-DMF suspension. The GeP-DMF suspension was ultrasonically treated for 2 h at a power of 250 W using an ultrasonic cleaner, and then ultrasonically treated for 5 h at a power of 400 W using an ultrasonic cell disruptor. Finally, centrifugation was carried out. First, centrifugation was carried out at a speed of 2000 rpm for 30 min, the supernatant was taken, and then centrifugation was carried out at a speed of 8000 rpm for 30 min, and the supernatant was taken to obtain GeP nanoparticles exfoliated by DMF, with a particle size distribution of about 68 nm. Then, rotary evaporation treatment was carried out in a water bath at a temperature of 70 °C and a rotation speed of 100 rpm. The concentration of GeP nanoparticles in the concentrated dispersion was 2 mg / mL -1 .

[0074] S2: The concentrated GeP nanoparticle dispersion and PVDF were added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at a speed of 300 rpm at 45 °C for 1 h until PVDF was completely dissolved and the GeP nanoparticles were uniformly dispersed. Among them, the mass fraction of PVDF was 10%, the mass ratio of N,N-dimethylformamide (DMF) to acetone was 2:1, and the GeP nanoparticles accounted for 1% of the solid mass in the GeP nanoparticle-PVDF composite dispersion

[0075] S3: The GeP nanoparticle-PVDF composite dispersion was placed in a 20 mL syringe for electrospinning to obtain a composite membrane. In this step, the electric field strength of electrospinning was 10 kV, the distance between the spinning needle and the collector was 10 cm, the injection speed of the syringe was 1.5 mL / h, and the rotation speed of the roller of the collection device was 500 rpm. Finally, the GeP nanoparticle-PVDF composite membrane was peeled off from the release paper and placed in an oven at 40 °C for 3 h to remove the residual solvent, and the GeP nanoparticle-PVDF composite piezoelectric film was prepared

[0076] Example 5

[0077] A preparation method of a GeP nanoparticle-PVDF composite piezoelectric film for a lithium metal battery, comprising the following steps:

[0078] S1: Weigh a certain mass of GeP sample and grind it in a mortar for 1.5 h. After grinding, add DMF solvent to obtain 1 mg / mL -1A total of 200 mL of GeP-DMF suspension. The GeP-DMF suspension was ultrasonicated for 3 h at a power of 400 W using an ultrasonic cleaner, and then ultrasonicated for 4 h at a power of 600 W using an ultrasonic cell disruptor. Finally, centrifugation was performed. First, centrifugation was carried out at a speed of 3000 rpm for 30 min, the supernatant was taken, and then centrifugation was carried out at a speed of 10000 rpm for 30 min, and the supernatant was taken to obtain GeP nanoparticles exfoliated by DMF, with a particle size distribution of about 68 nm. Then, rotary evaporation treatment was carried out in a water bath at a temperature of 90 °C and a rotation speed of 150 rpm. The concentration of GeP nanoparticles in the concentrated dispersion was 2 mg / mL -1 .

[0079] S2: The concentrated GeP nanoparticle dispersion and PVDF were added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at a speed of 300 rpm at 45 °C for 1 h until PVDF was completely dissolved and the GeP nanoparticles were uniformly dispersed. Among them, the mass fraction of PVDF was 15%, the mass ratio of N,N-dimethylformamide (DMF) to acetone was 2:1, and the GeP nanoparticles accounted for 3% of the solid mass in the GeP nanoparticle-PVDF composite dispersion

[0080] S3: The GeP nanoparticle-PVDF composite dispersion was put into a 20 mL syringe for electrospinning to obtain a composite membrane. In this step, the electric field strength of electrospinning was 15 kV, the distance between the spinning needle and the collector was 10 cm, the injection speed of the syringe was 1.5 mL / h, the rotation speed of the roller of the collection device was 500 rpm. Finally, the GeP nanoparticle-PVDF composite membrane was peeled off from the release paper and placed in an oven at 40 °C for 3 h to remove the residual solvent, and the GeP nanoparticle-PVDF composite piezoelectric film was prepared

[0081] Example 6

[0082] A preparation method of a GeP nanoparticle-PVDF composite piezoelectric film for a lithium metal battery, comprising the following steps:

[0083] S1: Weigh a certain mass of GeP sample and grind it in a mortar for 1 h. After grinding, add DMF solvent to obtain 1 mg / mL -1A total of 200 mL of GeP-DMF suspension. The GeP-DMF suspension was ultrasonically treated at a power of 300 W for 3 h using an ultrasonic cleaner, and then ultrasonically treated at a power of 500 W for 5 h using an ultrasonic cell disruptor. Finally, centrifugation was performed. First, centrifugation was carried out at a speed of 2500 rpm for 30 min, and the supernatant was taken. Then, centrifugation was carried out at a speed of 9000 rpm for 30 min, and the supernatant was taken to obtain GeP nanoparticles exfoliated by DMF, with a particle size distribution of about 68 nm. Then, rotary evaporation treatment was carried out in a water bath at a temperature of 80 °C and a rotation speed of 120 rpm. The concentration of GeP nanoparticles in the concentrated dispersion was 2 mg / mL -1 。

[0084] S2: The concentrated GeP nanoparticle dispersion and PVDF were added to a mixed solution of N,N-dimethylformamide and acetone, and magnetically stirred at a speed of 300 rpm at 45 °C for 1 h until PVDF was completely dissolved and the GeP nanoparticles were uniformly dispersed. Among them, the mass fraction of PVDF was 13%, the mass ratio of N,N-dimethylformamide (DMF) to acetone was 2:1, and the GeP nanoparticles accounted for 2.5% of the solid mass in the GeP nanoparticle-PVDF composite dispersion.

[0085] S3: The GeP nanoparticle-PVDF composite dispersion was placed in a 20 mL syringe for electrospinning to obtain a composite membrane. In this step, the electric field strength of electrospinning was 12 kV, the distance between the spinning needle and the collector was 10 cm, the injection speed of the syringe was 1.5 mL / h, and the rotational speed of the drum of the collection device was 500 rpm. Finally, the GeP nanoparticle-PVDF composite membrane was peeled off from the release paper and placed in an oven at 40 °C for 3 h to remove the residual solvent, and the GeP nanoparticle-PVDF composite piezoelectric film was prepared.

[0086] Figure 2 is the particle size distribution diagram of GeP nanoparticles prepared by the liquid-phase exfoliation method. It can be seen from the figure that the particle size of GeP nanoparticles prepared by the liquid-phase exfoliation method is mainly distributed around 68 nm.

[0087] Figure 3It is the scanning electron microscope characterization diagram of the piezoelectric thin films prepared in the above Comparative Example 1 and Examples 1 to 3. Among them, (a) is PVDF (sample of Comparative Example 1), (b) is 1% GeP / PVDF (sample of Example 1), (c) is 2% GeP / PVDF (sample of Example 2), and (d) is 3% GeP / PVDF (sample of Example 3). It can be seen from the figure that the prepared piezoelectric thin films all have a porous structure, and the GeP nanoparticles are uniformly mixed with PVDF. The fibers in the film are uniform in thickness, without beading, and the fiber diameter is between 500 - 1500 nm. Compared with PVDF fibers, as the content of GeP nanoparticles increases, the diameter of the GeP nanoparticle - PVDF composite fibers gradually increases.

[0088] Figure 4 It is the FTIR spectrogram of the piezoelectric thin films prepared in the above Comparative Example 1 and Examples 1 to 3. It can be seen from the figure that all four piezoelectric thin films have an α - phase peak at 763 cm -1 and β - phase peaks at 840 cm -1 , 1073 cm -1 , and 1280 cm -1 . The piezoelectric properties of PVDF are largely affected by the content of its internal β - phase. The amount of the β - phase directly determines the strength of the piezoelectric properties of PVDF. The content of the β - phase can be obtained from the following formula:

[0089]

[0090] where A α , A β are the peak intensities at 763 cm -1 and 840 cm -1 respectively. By calculation, the F β (%) values of the piezoelectric thin films prepared in Comparative Example 1 and Examples 1 to 3 are 56.7%, 63.2%, 74.2%, and 81% respectively. It can be seen that the composite of GeP nanoparticles and PVDF can effectively induce the formation of the β - phase in PVDF.

[0091] Figure 5 It is the test result of the piezoelectric voltage output of the piezoelectric thin films prepared in the above Comparative Example 1 and Examples 1 to 3. The prepared piezoelectric thin films are cut into square film pieces with a size of 3 * 3 cm 2 , and then clamped between two copper foil electrodes and encapsulated with Kapton tape. Under a stress of 20 N at 1 Hz, the maximum piezoelectric voltage outputs of the piezoelectric thin films of Comparative Example 1, Example 1, Example 2, and Example 3 are 2.5 V, 2.9 V, 3.6 V, and 4.5 V respectively. When the mass fraction of added GeP nanoparticles is 3%, the piezoelectric voltage output is the largest. It can be seen that adding GeP nanoparticles can increase the piezoelectric voltage output of the thin film.

[0092] Figure 6 are the test results of the piezoelectric current output of the piezoelectric films prepared in the above Comparative Example 1 and Examples 1-3. It can be seen from Figure 6 that under a stress of 20N 1Hz, the maximum piezoelectric current outputs of the piezoelectric films of Comparative Example 1, Example 1, Example 2, and Example 3 are 8nA, 8.2nA, 13nA, and 15nA respectively. When the mass fraction of GeP nanoparticles added is 3%, the piezoelectric current output is the largest. It can be seen that adding GeP nanoparticles can increase the piezoelectric current output of the film.

[0093] Figure 7 are the time-voltage test results of the lithium metal symmetric batteries prepared with the separator materials of the above Comparative Examples 1-2 and Example 3. The separator materials of Comparative Examples 1-2 and Example 3 were cut into circular pieces with a diameter of 19 mm using an MSK-T10 type cutting machine and dried overnight in a vacuum drying oven at 60°C. Inside a glove box filled with argon, a lithium metal symmetric battery was assembled in the order of Li negative electrode-separator-Li positive electrode and the time-voltage test was carried out. It can be seen from Figure 7 that under the condition of keeping other conditions of the lithium metal symmetric battery the same and only replacing different separator materials for testing, the voltage polarization of the lithium metal symmetric batteries assembled with the separator materials of Comparative Example 1 and Comparative Example 2 increased rapidly after cycling for about 350 h and 150 h respectively, while the polarization voltage of the lithium metal symmetric battery assembled with the 3% GeP / PVDF composite piezoelectric film prepared in Example 3 was only about 63 mV, and it could operate stably at an overpotential of 63 mV for up to 1000 h. This indicates that the 3% GeP / PVDF composite piezoelectric film prepared in Example 3 can effectively inhibit the growth of lithium dendrites and the generation of irreversible "dead lithium".

[0094] Figure 8 are the cycle performance test results of the lithium metal batteries prepared with the separator materials of the above Comparative Examples 1-2 and Example 3. The NCM811 cathode material, Ketjen black, and polyvinylidene fluoride were mixed in a mass ratio of 8:1:1, ground in an N-methylpyrrolidone solution to obtain a slurry, the slurry was coated on aluminum foil and dried, and then cut into circular pieces with a diameter of 14 mm using an MSK-T10 type cutting machine. Inside a glove box filled with argon, a lithium metal battery was assembled in the order of Li negative electrode-separator-NCM811 cathode and the cycle performance test was carried out. It can be seen from Figure 8It can be seen that, under the condition of keeping other conditions of the lithium metal battery the same, only different separator materials are replaced for testing. The capacity retention rates of the lithium metal batteries assembled with the separator materials of Comparative Example 1 and Comparative Example 2 are 60% and 53.4% respectively after 200 cycles, while the capacity retention rate of the lithium metal battery assembled with the 3% GeP / PVDF composite piezoelectric thin film prepared in Example 3 is as high as 76% after 200 cycles. This indicates that the lithium metal battery assembled with the 3% GeP / PVDF composite piezoelectric thin film prepared in Example 3 has excellent cycle stability.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A preparation method of GeP nanoparticle-PVDF composite piezoelectric film, characterized in that It includes the following steps: S1: Grind and pre-treat bulk GeP, and prepare a GeP nanoparticle dispersion by liquid-phase exfoliation method; then concentrate the GeP nanoparticles by rotary evaporation; S2: Add the concentrated GeP nanoparticle dispersion to the PVDF solution, stir evenly to obtain a GeP nanoparticle-PVDF composite dispersion; S3: Use the GeP nanoparticle-PVDF composite dispersion for electrospinning to prepare the GeP nanoparticle-PVDF composite piezoelectric thin film.

2. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, characterized in that In step S1, during the grinding pre-treatment process, the grinding time is 0.8 - 1.5 h.

3. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, characterized in that In step S1, during the liquid-phase exfoliation process, specifically: first, treat the DMF suspension of GeP with an ultrasonic cleaner, then continue ultrasonic exfoliation with an ultrasonic cell disruptor, and finally perform centrifugation to obtain the GeP nanoparticle dispersion.

4. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric film according to claim 3, characterized in that Treat the DMF suspension of GeP with an ultrasonic cleaner, then continue ultrasonic exfoliation with an ultrasonic cell disruptor, and finally perform centrifugation to obtain the GeP nanoparticle dispersion, specifically: first, ultrasonically treat the DMF suspension of GeP with an ultrasonic cleaner at a power of 250 - 400 W for 2 - 3 h, then perform ultrasonic exfoliation treatment with an ultrasonic cell disruptor at a power of 400 - 600 W for 2 - 5 h, and finally perform centrifugation treatment; during the centrifugation treatment process, first centrifuge at a speed of 2000 - 3000 rpm for 30 min, take the supernatant, and then centrifuge the supernatant at a speed of 8000 - 10000 rpm for 30 min to obtain the GeP nanoparticle dispersion.

5. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, characterized in that, In step S1, during the rotary evaporation process, the temperature is 70 - 90 °C and the rotation speed is 100 - 150 rpm.

6. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, wherein, In step S2, the preparation process of the GeP nanoparticle-PVDF composite dispersion is: add the concentrated GeP nanoparticle dispersion and PVDF to a mixed solution of N,N-dimethylformamide and acetone, and stir until PVDF is completely dissolved and the GeP nanoparticles are evenly dispersed to obtain the GeP nanoparticle-PVDF composite dispersion.

7. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, characterized in that, In the GeP nanoparticle-PVDF composite dispersion, the mass fraction of PVDF is 10% - 15%, and the GeP nanoparticles account for 1% - 3% of the solid mass in the GeP nanoparticle-PVDF composite dispersion.

8. The preparation method of a GeP nanoparticle-PVDF composite piezoelectric thin film according to claim 1, wherein, In step S3, during the electrospinning process, the electric field strength is 10 - 15 kV.

9. A GeP nanoparticle-PVDF composite piezoelectric thin film, characterized in that, Prepared by the method according to any one of claims 1 - 8.

10. Use of a GeP nanoparticle-PVDF composite piezoelectric thin film as described in claim 9 in a lithium metal battery, characterized in that, Use the described GeP nanoparticle-PVDF composite piezoelectric thin film as a battery separator; the piezoelectric output voltage of the piezoelectric device assembled with this composite film is 2.9 - 4.5 V.

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