Ag@amorphous C nanoparticles, PVDF-based composite film and preparation method thereof

Abstract

The present invention discloses a composite film of Ag@amorphous carbon nanoparticles and PVDF-based materials, and a method for preparing the same. The present invention employs an arc discharge method to synthesize Ag@amorphous carbon core-shell nanoparticles in a single step, further yielding a PVDF / Ag@amorphous carbon composite film. This polymer film addresses the existing problem of metal (Ag)-doped polymer film capacitors, which suffer from particle agglomeration and significant conductivity loss when attempting to achieve a high dielectric constant.

Description

Technical Field

[0001] The present invention relates to the field of dielectrics, and in particular to Ag@amorphous C nanoparticles, a PVDF-based composite film and a preparation method thereof. Background Art

[0002] Dielectric materials play a key role in electronic devices, storing charge and energy. The ever-increasing demand for electrification demands advanced dielectric materials, including high capacitance density, high energy density, high current handling capability, high voltage, high temperature, high thermal conductivity, lightweight design, and environmental reliability. Consequently, nanodielectric engineering has emerged and attracted widespread attention worldwide. The 21st century's growing demand for power and electrification has put dielectric materials in the spotlight as never before on the global stage.

[0003] As fundamental passive components in power and electronic devices, capacitors account for over 25% of a circuit's volume and provide crucial functions such as pulse power, power regulation, energy storage, circuit protection, and signal filtering and processing. From a capacitor's structural perspective, the dielectric between the two layers of metal electrodes is the core energy storage material. Capacitors can be categorized into four main types, depending on the dielectric material: supercapacitors, electrolytic capacitors, ceramic capacitors, and film capacitors. Film capacitors, with their advantages of fast discharge, high voltage resistance, excellent reliability, light weight, and low cost, play a vital role in advanced electronic devices and power systems.

[0004] However, the low dielectric strength and energy density of polymer dielectrics in film capacitors greatly limit the development of film capacitors in future applications. For example, the commercially widely used polymer dielectric biaxially oriented polypropylene (BOPP) has an energy density of only about 2 J / cm due to its low dielectric strength. -3 , which makes its practical application cumbersome in terms of volume and cost. Polyvinylidene fluoride (PVDF)-based polymers have attracted widespread attention due to their high dielectric constant and potential for preparing high-performance thin film capacitors.

[0005] Since the energy density of thin film capacitors is closely related to the dielectric constant and breakdown strength of polymers, many researchers have increased the dielectric constant of polymers by doping them with inorganic ceramics or metal particles. However, to obtain polymer dielectrics with higher dielectric constants, it is generally necessary to dope them with higher volume fractions of inorganic ceramic fillers or metal particle fillers. However, a high filling amount will inevitably cause some inevitable defects and agglomeration of particles in the polymer matrix, which will lead to a significant decrease in the breakdown field strength of the thin film dielectric. At the same time, too many metal particles can easily form a conductive path and produce large conductivity losses, resulting in the current dielectrics being at a low energy storage density and energy storage efficiency. Summary of the Invention

[0006] In order to solve the problem in the prior art of polymer film capacitors doped with metal particles (Ag) fillers that particles agglomerate and cause large conductivity loss when obtaining a high dielectric constant, the present invention provides a method for synthesizing modified Ag@amorphous C core-shell nanoparticles and a solution for preparing PVDF / Ag@amorphous C core-shell nanoparticle composite films.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] First, the present invention provides a method for preparing Ag@amorphous C nanoparticles, comprising the following steps:

[0009] (1) Preparation of anode graphite rod: Ag powder and graphite powder are mixed and dried uniformly, filled into a hollowed graphite rod, compacted, and placed in a muffle furnace for heating and curing;

[0010] (2) Arc synthesis of modified Ag@amorphous C core-shell nanoparticles: Install cathode and anode graphite rods, evacuate, pass helium, introduce liquid precursor, perform arc reaction, and collect the product.

[0011] In the above-described method for preparing Ag@amorphous carbon nanoparticles, preferably, in step (1), the mass ratio of Ag powder to graphite powder is 1:4-8. By varying the Ag / C ratio, the thickness of the Ag core and amorphous carbon shell can be controlled to obtain different carbon shell and Ag core sizes, thereby customizing fillers with different dielectric properties.

[0012] In the above-mentioned method for preparing Ag@amorphous C nanoparticles, preferably, a graphite binder and anhydrous ethanol are added in step (1). Anhydrous ethanol facilitates the mixing and granulation of graphite powder and silver powder, while the graphite binder helps the two powders to be more tightly bonded during the sintering process.

[0013] In the above-mentioned method for preparing Ag@amorphous C nanoparticles, preferably, the temperature control program for heating and curing in the muffle furnace in step (1) is: heating at 120-140°C for 3-5 hours in the first stage, then heating at 250-270°C for 1-3 hours in the second stage, and cooling in the furnace; more preferably, the temperature control program for heating and curing in the muffle furnace is heating at 130°C for 4 hours in the first stage, then heating at 260°C for 2 hours in the second stage, and cooling in the furnace. At the same time, the heating rate is 3-6°C / min before reaching the first stage temperature, and the heating rate is 8-12°C / min before reaching the second stage temperature.

[0014] In the above-mentioned method for preparing Ag@amorphous C nanoparticles, preferably, the liquid precursor in step (2) includes at least one of deionized water, ethanol, and acetonitrile, which can be deionized water or deionized water / ethanol or deionized water / acetonitrile or water / ethanol / acetonitrile. There are many ways to introduce the liquid precursor, such as droplet mode, atomization mode, or vaporization mode. This can be well achieved by adding one or more spray devices connected to a liquid pipeline to the reaction device or placing a crucible filled with liquid precursor just below the center of the arc (i.e., liquid vaporization mode); when the liquid precursor is a single liquid, it can be introduced into a liquid pipeline. When the liquid precursor is two or more liquids, they can be introduced into the spray devices connected to their respective liquid pipelines or can be introduced into a liquid pipeline at the same time, as long as liquid atomization can be achieved. Preferably, the arc reaction time in step (2) is 1-3 minutes.

[0015] In the present invention, step (1) muffle furnace heating and curing only combines the graphite powder and the Ag powder more tightly, which is conducive to the stable arc discharge and does not form nanoparticles. Step (2) arc reaction itself heats the silver and graphite powder into a plasma state, which has the function of forming carbon-coated silver (Ag@C) core-shell nanoparticles. At the same time, a liquid precursor is introduced during the arc reaction. The liquid precursor can be heated to a plasma state and introduced to obtain modified (containing a large number of carboxyl groups and / or hydroxyl groups, etc.) Ag@amorphous C nanoparticles.

[0016] Typically, an arc reaction involves a cathode and an anode. The cathode is a pure graphite rod, and the anode is filled with graphite powder and silver powder. The arc reaction consumes the raw materials in the anode graphite rod, forming a composite material. However, directly subjecting the arc reaction to the arc reaction without introducing a liquid precursor primarily yields a core-shell nanostructure composed of graphite coated with Ag. The resulting graphite shell is conductive, which is detrimental to the dielectric properties of the film. Introducing a liquid precursor can provide reactive groups, and ethanol and acetonitrile can also participate in the reaction to form an amorphous carbon shell. This helps regulate the thickness of the amorphous carbon shell and adjust the plasma etching efficiency, providing more active sites for the formation of functional groups such as carboxyl groups. Introducing a liquid precursor during the arc discharge process allows for the one-step synthesis of Ag@amorphous C core-shell nanoparticles surface-modified with carboxyl groups. These reactive groups enhance the dispersion stability of the Ag@amorphous C core-shell particles in PVDF, helping to improve the dielectric properties of the film. By introducing a liquid precursor, a spray device can be set near the center of the arc to emit the liquid in the form of extremely small particles toward the center of the arc.

[0017] Secondly, by adopting the above preparation method of the present invention, Ag@amorphous C nanoparticles can be obtained, wherein the amorphous C shell is uniformly wrapped on the surface of the Ag core, such as Figure 1The amorphous C shell is evenly wrapped on the surface of the Ag core, which can effectively block the migration of interlayer electrons and thus reduce the conductivity loss.

[0018] Thirdly, the present invention also provides a PVDF-based composite film, which is mainly composed of PVDF and the above-mentioned Ag@amorphous C nanoparticles.

[0019] Fourthly, the present invention also provides a method for preparing the PVDF-based composite film, which comprises the following steps: (1) preparing a casting solution: dispersing Ag@amorphous C nanoparticles in DMF, adding PVDF to the dispersion, heating and stirring until the PVDF is completely dissolved, and vacuum degassing to obtain a casting solution;

[0020] (2) Preparation of PVDF composite film: pour the casting liquid onto the casting plate, scrape it into a film, dry it, and demould it.

[0021] In the above-mentioned method for preparing the PVDF-based composite film, preferably, the molecular weight Mw of the PVDF is 100,000-800,000, more preferably 200,000-600,000. The heating and stirring temperature is 60-80°C.

[0022] In the above-mentioned method for preparing the PVDF-based composite film, preferably, in the casting solution, the content of Ag@amorphous C nanoparticles is 2-10 wt%, and the content of PVDF is 8-12 wt%.

[0023] The modified Ag@amorphous C core-shell nanoparticles described in this invention are synthesized in a single step using an arc discharge method, which is considered a simple, safe, and pollution-free method for preparing core-shell nanoparticles. The preparation method for the PVDF / Ag@amorphous C composite film is simple. The arc discharge equipment does not require a high vacuum level, and the film formation process can be carried out at ambient pressure. Conventional reagents are used, making it easy to implement on an industrial scale.

[0024] The inventors have found that the conventional direct arc reaction between graphite powder and silver powder (without the introduction of liquid precursor) only produces graphite-coated silver nanoparticles. The graphite shell produced by this method has conductivity, which is not conducive to the dielectric properties of the film ( Figure 3 The XRD graphite (002) peak intensity and Raman I D / I G The value of indicates that the shell of the unmodified core-shell particles is mainly composed of graphite, and the carbon shell after modification is mainly composed of amorphous carbon) Unmodified particles I D / I G The value of the modified particles is 0.356. D / I GThe value is 0.805. The larger the value, the greater the amorphous carbon content in the particles. At the same time, our modification method generates carboxyl functionalized amorphous carbon coated silver nanoparticles. The introduction of carboxyl groups can improve the dispersion of core-shell nanoparticles in PVDF ( Figure 2 ), the amorphous carbon of the outer shell is beneficial to the dielectric properties of the film. At the same time, the Ag@amorphous C core-shell nanoparticles in the present invention are prepared in one step by an arc discharge method. The present invention obtains modified Ag@amorphous C core-shell nanoparticles by designing the type of liquid precursor. In addition, the composite film of the present invention is formed by blending PVDF, modified Ag@amorphous C core-shell nanoparticles and DMF solution and heating them. After modification, the surface of the Ag@amorphous C nanoparticles contains a large number of carboxyl functional groups. These modified functional groups can improve the dispersibility and stability of the filler in the PVDF matrix, reduce the agglomeration of nanoparticles, thereby significantly reducing the leakage current in the film, improving the breakdown strength and obtaining a high energy density composite film. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Figure 1 is a structural diagram of the modified Ag@amorphous C core-shell nanoparticles of the present invention; (a) is a schematic diagram, and (b) is a transmission electron micrograph;

[0026] Figure 2 These are enlarged images of the unmodified membrane of Example 1 and the modified membrane obtained in Example 1; (a) is the unmodified Ag@graphite C and PVDF composite membrane of Example 1, and (b) is the modified Ag@amorphous C and PVDF composite membrane of Example 1; it can be seen from the figure that the nanoparticles of the modified membrane are evenly dispersed, while the nanoparticles of the unmodified membrane are agglomerated.

[0027] Figure 3The following are the test patterns of the unmodified PVDF composite membrane of Example 1 and the modified PVDF composite membrane of Example 1; (a) is XRD detection, and (b) is Raman detection; the XRD results of the unmodified Ag@graphite C nanoparticles and the modified Ag@amorphous C nanoparticles show that at 2θ = 26.5°, i.e., the (002) crystal plane of graphite, the two samples produce a large difference. It is obvious that the peak intensity of the graphite (002) crystal plane in the unmodified particles is very high and sharp, while the intensity of this peak in the modified particles is very weak. Since the intensity of the (002) peak is proportional to the degree of graphitization of the material, it can be used to characterize the degree of graphitization of the carbon material. Therefore, it can be judged that the carbon shell of the carbon-coated silver nanoparticles in the unmodified particles is mainly composed of graphite, while the degree of graphitization of the carbon shell component after the modification treatment is greatly reduced, with amorphous carbon being the main component. Raman spectroscopy clearly shows a significant increase in the D peak of the modified Ag@amorphous C nanoparticles, and the ID / IG ratio increases from 0.356 (unmodified Ag@graphite C nanoparticles) to 0.805. This significant increase in the ID / IG ratio of the modified Ag@amorphous C nanoparticles also indicates a decrease in the degree of graphitization of the carbon shell and a significant increase in the amorphous carbon content, a result that echoes the XRD results.

[0028] Figure 4 This is a comparison of the dielectric properties of the unmodified PVDF / Ag@graphite C composite film of Example 1 and the modified PVDF / Ag@amorphous C composite film of Example 1, wherein (a) is the dielectric loss, (b) is the dielectric strength, and (c) is the breakdown strength. The results show that the dielectric constant of the modified film is always higher than that of the unmodified film, and the dielectric loss of the modified PVDF composite film is 0.0226 (103Hz) which is 50.4% lower than the dielectric loss of the unmodified PVDF composite film of 0.0456 (103Hz). In terms of breakdown strength, the modified PVDF composite film also has a better breakdown strength of 623.0KV / cm, which is 330% of the breakdown strength of the unmodified film. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to specific embodiments.

[0030] The method for preparing the PVDF / Ag@amorphous C composite film of the present invention may include the following steps: (1) preparing an anode electrode: taking a certain proportion of silver powder and graphite powder, thoroughly mixing them, adding a certain proportion of graphite binder and anhydrous ethanol, and stirring them evenly. The mixture is allowed to stand at room temperature for a period of time until the anhydrous ethanol evaporates until the mixed powder exhibits a granular texture, and the mixture is filled into a prepared hollowed-out graphite rod and fully compacted.

[0031] (2) Curing raw materials: Place the graphite rod in a muffle furnace for heating and curing. The temperature control program is to heat at 130°C for 4 hours and then heat at 260°C for 2 hours. After cooling to room temperature, the anode electrode for arc reaction is obtained.

[0032] (3) Synthesis of Ag@amorphous C nanoparticles: Install the anode and cathode graphite rods (with conical tips) on the arc reaction device, control the distance between the anode and cathode to be about 1 mm, place the collection cover, close the reactor, turn on the power switch, pump the reaction chamber pressure to several Pa, turn on the cooling water, turn off the pressure sensor, introduce the liquid precursor (a spray device is provided just above the center of the arc, which can emit the liquid in the form of extremely small particles toward the center of the arc), and slowly reduce the distance between the two electrodes through the stepping device until an arc reaction occurs. After the reaction time is over, turn off the power, wait for the chamber to cool to room temperature, and then open the device to collect the product.

[0033] (4) Preparation of casting solution: Ag@amorphous C nanoparticles obtained in step (1) were dispersed in DMF according to different weights, ultrasonicated for 1 h, a certain amount of PVDF (Mw = 400000) was added to the dispersion, stirred at 70 ° C until PVDF was completely dissolved, and degassed under vacuum conditions for 1 h.

[0034] (5) Preparation of PVDF / Ag@amorphous C nanoparticle composite film: The casting solution obtained in step (4) was poured onto a clean, smooth glass plate, and the film was evenly scraped with a scraper. The film was placed in a 40°C oven and dried for 12 h. The glass plate was then immersed in deionized water until it fell off to obtain a composite film.

[0035] Example 1

[0036] (1) Preparation of anode electrode: Take 6 g of silver powder and graphite powder in a mass ratio of 1:6, mix thoroughly, add graphite binder and an appropriate amount of anhydrous ethanol, and stir evenly. Let it stand at room temperature for a while to allow the anhydrous ethanol to air-dry until the mixed powder has a granular texture. Fill the prepared hollowed-out graphite rod (graphite rod 50 mm × φ10 mm, hole 30 mm × φ8 mm) and fully compact it.

[0037] (2) Curing the raw materials: Place the graphite rod in a muffle furnace for heating and curing. The temperature control program is to heat at 130℃ for 4 hours and then at 260℃ for 2 hours. After the temperature of the muffle furnace cools down to room temperature, the anode electrode for the arc reaction is obtained. (3) Synthesis of Ag@amorphous C nanoparticles: Install the anode and cathode graphite rods (with conical tips) on the arc reaction device. Control the distance between the anode and cathode to be about 1mm. Turn on the power switch, pump the pressure in the reaction chamber to a low vacuum state, turn on the cooling water, introduce liquid precursor deionized water (a spray device is provided near the center of the arc to spray the liquid into the center of the arc in the form of extremely small particles), and slowly reduce the distance between the two electrodes by the stepping device until an arc reaction occurs. After the reaction time is over, turn off the power supply. Wait for the chamber to cool down to room temperature and then open the device to collect the product.

[0038] (4) Preparation of casting solution: The modified Ag@amorphous C nanoparticles obtained in step (3) were dispersed in N,N-dimethylformamide (DMF) at different weights, ultrasonicated for 1 h, and a certain amount of PVDF (Mw = 400000) was added to the dispersion. The mixture was stirred at 70 ° C until the PVDF was completely dissolved. The mixture was degassed under vacuum conditions for 1 h to obtain 5 g of casting solution with a content of 2 wt% of Ag@amorphous C nanoparticles and a mass fraction of 10 wt% of PVDF.

[0039] (5) Preparation of PVDF / Ag@amorphous C nanoparticle composite films: The casting solution was poured onto a clean, smooth glass plate and evenly scraped with a scraper to form a film. The film was then dried in a 40°C oven for 12 h. The glass plate was then immersed in deionized water until it fell off to form a composite film. Finally, gold electrodes were plated on the upper and lower surfaces of the composite film for subsequent dielectric property testing.

[0040] Comparative Example 1

[0041] (1) Same as Example 1;

[0042] (2) Same as Example 1;

[0043] (3) Synthesis of Ag@graphite C nanoparticles: No liquid precursor deionized water was introduced, and the rest was the same as in Example 1.

[0044] (4) Preparation of casting solution: Ag@graphite C nanoparticles obtained in step (3) were dispersed in N,N-dimethylformamide (DMF) according to different weights, ultrasonicated for 1 h, a certain amount of PVDF (Mw = 400000) was added to the dispersion, stirred at 70 ° C until PVDF was completely dissolved, and degassed under vacuum conditions for 1 h to obtain a casting solution.

[0045] (5) Preparation of PVDF / Ag@graphite C nanoparticle composite film: Pour the casting solution onto a clean, smooth glass plate, scrape it evenly with a scraper to form a film, put it into a 40°C oven and dry it for 12 h. Then, soak the glass plate in deionized water until it falls off to obtain a composite film.

[0046] Through Example 1 and Comparative Example 1, under the same Ag@C doping amount (2wt%) conditions, the dielectric properties test of the unmodified (no carboxyl group) Ag@C core-shell nanoparticles of Comparative Example 1 and the modified (carboxyl group) Ag@C core-shell nanoparticles of Example 1 showed that the modified Ag@C core-shell nanoparticles had a higher dielectric constant and significantly reduced dielectric loss. The breakdown strength of the modified film was nearly 330% of that of the unmodified film.

[0047] Example 2

[0048] (1) Same as Example 1;

[0049] (2) Same as Example 1;

[0050] (3) Synthesis of Ag@amorphous C nanoparticles: Install the anode and cathode graphite rods (with conical tips) on the arc reaction device, control the distance between the anode and cathode to be about 1 mm, turn on the power switch, pump the reaction chamber pressure to a low vacuum state, turn on the cooling water, introduce the liquid precursor (deionized water / ethanol) (a spray device is provided near the center of the arc, which can emit the liquid in the form of extremely small particles toward the center of the arc), and slowly reduce the distance between the two electrodes through the stepping device until an arc reaction occurs. After the reaction time is over, turn off the power, wait for the chamber to cool to room temperature, and then open the device to collect the product.

[0051] (4) Same as Example 1;

[0052] (5) Same as Example 1.

[0053] Example 3

[0054] (1) Same as Example 1;

[0055] (2) Same as Example 1;

[0056] (3) Synthesis of Ag@amorphous C nanoparticles: Install the anode and cathode graphite rods (with conical tips) on the arc reaction device, control the distance between the anode and cathode to be about 1 mm, introduce the liquid precursor (deionized water / acetonitrile) (a spray device is provided near the center of the arc, which can emit the liquid in the form of extremely small particles toward the center of the arc), turn on the power switch, pump the reaction chamber pressure to a low vacuum state, turn on the cooling water, and slowly reduce the distance between the two electrodes through the stepping device until an arc reaction occurs. After the reaction time is over, turn off the power, wait for the chamber to cool to room temperature, and then open the device to collect the product.

[0057] (4) Same as Example 1;

[0058] (5) Same as Example 1.

[0059] Example 4

[0060] Step (1) silver powder and graphite powder were prepared in a mass ratio of 1:4, and the other conditions were the same as those in Example 1 to obtain a PVDF / Ag@amorphous C nanoparticle composite film.

[0061] Example 5

[0062] Step (1) silver powder and graphite powder were prepared in a mass ratio of 1:8, and the other conditions were the same as those in Example 1 to obtain a PVDF / Ag@amorphous C nanoparticle composite film.

[0063] This invention, for the first time, utilizes an arc discharge method to synthesize carboxyl-functionalized amorphous carbon-coated Ag core-shell nanoparticles in a single step. Using these nanofillers, a novel PVDF composite film with excellent dielectric properties is synthesized. The introduction of a liquid precursor during the arc discharge process allows for the first time to control the insulating properties of the carbon shell of the synthesized amorphous carbon-coated silver nanoparticles (Ag@C) during the arc discharge process. The unmodified graphite-like carbon shell is then transformed into an amorphous carbon-like shell. Furthermore, a large number of carboxyl functional groups are grafted onto the surface of the modified amorphous carbon shell, effectively improving the nanoparticle's dispersibility in PVDF. These improvements contribute to improving the dielectric constant and breakdown voltage of the composite film, while also achieving lower dielectric loss.

[0064] It should be noted that the technical contents of the present invention described above are only for the purpose of explaining and illustrating the technical essence of the present invention to enable those skilled in the art to understand the technical essence of the present invention. Therefore, the technical contents described above are not intended to limit the substantial protection scope of the present invention. The substantial protection scope of the present invention shall be based on the claims. Those skilled in the art should be aware that any modifications, equivalent substitutions, and improvements based on the substantial spirit of the present invention shall fall within the substantial protection scope of the present invention.

Claims

1. A PVDF-based composite film, mainly composed of PVDF and Ag@amorphous C nanoparticles, wherein the amorphous C shell is uniformly wrapped around the surface of the Ag core; the preparation method of the Ag@amorphous C nanoparticles comprises the following steps: (1) Preparation of anode graphite rod: Ag powder and graphite powder are mixed evenly, filled into the hollowed graphite rod, compacted, and placed in a muffle furnace for heating and curing; (2) Arc synthesis of modified Ag@amorphous C core-shell nanoparticles: install cathode and anode graphite rods, evacuate, pass helium, introduce liquid precursor, perform arc reaction, and collect products; the liquid precursor includes at least one of deionized water, ethanol, and acetonitrile.

2. The PVDF-based composite film according to claim 1, wherein Step (1) The mass ratio of Ag powder to graphite powder is 1:4-8.

3. The PVDF-based composite film according to claim 1, wherein In step (1), a graphite binder and anhydrous ethanol are added.

4. The PVDF-based composite film according to claim 1, wherein The temperature control program for heating and curing in the muffle furnace in step (1) is heating at 120-140°C for 3-5 hours and then heating at 250-270°C for 1-3 hours, followed by cooling in the furnace.

5. The PVDF-based composite film according to claim 4, characterized in that: The temperature control program for heating and curing in the muffle furnace in step (1) is heating at 130°C for 4 hours and then heating at 260°C for 2 hours, followed by cooling in the furnace.

6. The PVDF-based composite film according to claim 1, wherein: In step (2), the liquid precursor is water, or water and ethanol, or water and acetonitrile, or water, ethanol and acetonitrile.

7. The method for preparing the PVDF-based composite film according to any one of claims 1 to 6, comprising the following steps: (1) Preparation of casting solution: Ag@amorphous C nanoparticles were dispersed in DMF, PVDF was added to the dispersion, heated and stirred until PVDF was completely dissolved, and vacuum degassing was performed to obtain the casting solution; (2) Preparation of PVDF composite film: Pour the casting liquid onto the casting plate, scrape it into a film, dry it and demould it.

8. The preparation method according to claim 7, wherein The PVDF molecular weight Mw=100,000-800,000.

9. The preparation method according to claim 8, wherein The PVDF molecular weight Mw=200,000-600,000.

10. The preparation method according to claim 7, wherein In the casting solution, the content of Ag@amorphous C nanoparticles is 2-10 wt %, and the content of PVDF is 8-12 wt %.

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