Polyvinylidene fluoride dielectric composite film, preparation method and application thereof

Abstract

The application belongs to the field of polymer films, and discloses a polyvinylidene fluoride dielectric composite film and a preparation method and application thereof, which comprises the following steps: mixing N, N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer to obtain a mixed system solution; and solidifying the mixed system solution into a film to obtain the polyvinylidene fluoride dielectric composite film. In the polyvinylidene fluoride dielectric composite film added with the calcium sulfate ion oligomer, the dielectric constant of the composite film is obviously increased, and the dielectric loss is not obviously increased. The polyvinylidene fluoride dielectric composite film with dielectric multifunction is prepared to replace traditional ceramic dielectric materials, the preparation method is simple and convenient to operate, the polyvinylidene fluoride dielectric composite film is endowed with excellent dielectric performance and high-temperature resistance, and can be widely applied in the fields of pressure sensors, lithium ion batteries, automobile motors and high-temperature resistant thermistor devices.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of polymer film, and relates to a polyvinylidene fluoride dielectric composite film and a preparation method and application thereof. BACKGROUND

[0002] Functionalization of polymer film materials has been widely concerned, and polymer materials with special properties have become the research focus. Polyvinylidene fluoride is a polymorphic semi-crystalline polymer, and the most common crystal forms thereof are three, namely, alpha crystal form, beta crystal form and gamma crystal form. Among them, the alpha crystal form of polyvinylidene fluoride has excellent mechanical properties, and can be used in electronics, chemical industry and solar devices. The beta crystal form and gamma crystal form of polyvinylidene fluoride have good piezoelectric and ferroelectric effects, and are widely used in transducer devices in various fields, such as pressure-sensitive devices and humidity-sensitive devices, and can be applied in storage devices and intelligent electrical appliances.

[0003] However, it is currently difficult to prepare polyvinylidene fluoride with high content of beta crystal form and gamma crystal form, and the steps are complex and time-consuming. SUMMARY

[0004] The present application aims to overcome the shortcomings of the prior art, and provides a polyvinylidene fluoride dielectric composite film and a preparation method and application thereof.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] In a first aspect, the present application provides a preparation method of a polyvinylidene fluoride dielectric composite film, comprising: mixing N,N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer to obtain a mixed system solution; and solidifying the mixed system solution into a film to obtain the polyvinylidene fluoride dielectric composite film.

[0007] Optionally, the method further comprises: adding triethylamine to an alcohol solution of CaCl2·2H2O and stirring to obtain a mixed solution A; adding an alcohol solution of H2SO4 to the mixed solution A and stirring to obtain a mixed solution B; centrifuging the mixed solution B, and washing the centrifuged polymer with ethanol to remove residual triethylamine to obtain the calcium sulfate ion oligomer.

[0008] Optionally, the mass fraction ratio of Ca to triethylamine in the mixed solution A is 1:5-1:50.

[0009] Optionally, in the mixed system solution, the total mass concentration of polyvinylidene fluoride and calcium sulfate ion oligomer is 3%-7%, and the mass fraction of the calcium sulfate ion oligomer is 0.1%-1% of the polyvinylidene fluoride.

[0010] Optionally, the mixing N,N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer comprises: mixing N,N-dimethylformamide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; adding calcium sulfate ion oligomer into the polyvinylidene fluoride solution and stirring to obtain a mixed system solution.

[0011] Optionally, the adding calcium sulfate ion oligomer into the polyvinylidene fluoride solution and stirring comprises: adding calcium sulfate ion oligomer into the polyvinylidene fluoride solution at 35-40℃ and stirring uniformly at 1000-5000r / min under magnetic stirring.

[0012] Optionally, the solidifying the mixed system solution into a film comprises: dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven.

[0013] Optionally, the dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven comprises: dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven at 90-120℃.

[0014] In the second aspect of the present application, a polyvinylidene fluoride dielectric composite film is provided, which is prepared by the above-mentioned polyvinylidene fluoride dielectric composite film preparation method.

[0015] In the third aspect of the present application, the above-mentioned polyvinylidene fluoride dielectric composite film is applied to the preparation of a high-temperature-resistant thermistor device.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The polyvinylidene fluoride dielectric composite film preparation method of the present application first prepares a mixed system solution with N,N-dimethylformamide as a solvent and a solute of polyvinylidene fluoride and calcium sulfate ion oligomer, and then solidifies the mixed system solution into a film to obtain a polyvinylidene fluoride dielectric composite film. Through detection and comparison, it is found that in the polyvinylidene fluoride dielectric composite film with added calcium sulfate ion oligomer, the dielectric constant of the composite film is significantly increased, and the dielectric loss is not significantly increased. The present application replaces the traditional ceramic dielectric material by preparing a polyvinylidene fluoride dielectric composite film with multiple dielectric functions, and the preparation method is simple and easy to operate, which endows the polyvinylidene fluoride dielectric composite film with excellent dielectric properties and high-temperature resistance, and can be widely applied in the fields of pressure sensors, lithium ion batteries, automobile motors and high-temperature-resistant thermistor devices, etc. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The Fourier infrared spectrum of the polyvinylidene fluoride dielectric composite film doped with calcium sulfate ion oligomer with different degrees of polymerization in the embodiments of the present application.

[0019] Figure 2 The Fourier infrared spectrum of the polyvinylidene fluoride dielectric composite film doped with the calcium sulfate ion oligomer of different contents of the embodiment of the present application.

[0020] Figure 3 The dielectric constant graph of the polyvinylidene fluoride dielectric composite film doped with the calcium sulfate ion oligomer of different polymerization degrees of the embodiment of the present application.

[0021] Figure 4 The dielectric loss graph of the polyvinylidene fluoride dielectric composite film doped with the calcium sulfate ion oligomer of different polymerization degrees of the embodiment of the present application.

[0022] Figure 5 The dielectric constant graph of the polyvinylidene fluoride dielectric composite film doped with the calcium sulfate ion oligomer of different contents of the embodiment of the present application.

[0023] Figure 6 The dielectric loss graph of the polyvinylidene fluoride dielectric composite film doped with the calcium sulfate ion oligomer of different contents of the embodiment of the present application.

[0024] Figure 7 The ultraviolet visible light transmittance graph of the pure polyvinylidene fluoride film, the polyvinylidene fluoride film doped with CaSO4 powder and the polyvinylidene fluoride film doped with the calcium sulfate ion oligomer of the embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the personnel in the art better understand the present application scheme, the technical scheme in the embodiment of the present application will be described clearly and completely in the following with reference to the drawings in the embodiment of the present application. Obviously, the described embodiment is only a part of the embodiment of the present application, not all. Based on the embodiment in the present application, all other embodiments obtained by the ordinary skilled in the art without creative labor should belong to the scope of the present application.

[0026] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0027] The application will be described in further detail below with reference to the drawings:

[0028] In an embodiment of the application, a preparation method of a polyvinylidene fluoride dielectric composite film is provided, in particular, a preparation method of a calcium sulfate ion oligomer doped polyvinylidene fluoride dielectric composite film, which has the characteristics of low reaction temperature, short time and easy industrialization.

[0029] Specifically, the preparation method of the polyvinylidene fluoride dielectric composite film comprises the following steps:

[0030] The N,N-dimethylformamide, the polyvinylidene fluoride and the calcium sulfate ion oligomer are mixed to obtain a mixed system solution; and the mixed system solution is solidified into a film to obtain the polyvinylidene fluoride dielectric composite film.

[0031] The preparation method of the polyvinylidene fluoride dielectric composite film of the application first uses N,N-dimethylformamide as a solvent to prepare a mixed system solution with the solute being polyvinylidene fluoride and calcium sulfate ion oligomer, and then solidifies the mixed system solution into a film to obtain the polyvinylidene fluoride dielectric composite film. It is found through detection and comparison that the dielectric constant of the composite film is obviously increased in the polyvinylidene fluoride dielectric composite film with the addition of the calcium sulfate ion oligomer, and the dielectric loss is not obviously increased. The polyvinylidene fluoride dielectric composite film with multiple functions of dielectricity is prepared to replace the traditional ceramic dielectric material in the application, the preparation method is simple and easy to operate, the polyvinylidene fluoride dielectric composite film is endowed with excellent dielectric properties and high temperature resistance, and can be widely applied in the fields of pressure sensors, lithium ion batteries, automobile motors and high temperature resistant thermistor devices.

[0032] In a possible implementation, a feasible preparation method of the calcium sulfate ion oligomer is provided, the calcium sulfate ion oligomer can be prepared by the preparation method, or can be directly purchased.

[0033] Specifically, the preparation method of the calcium sulfate ion oligomer comprises: adding triethylamine to an alcohol solution of CaCl2·2H2O and stirring to obtain a mixed solution A; adding an alcohol solution of H2SO4 to the mixed solution A and stirring to obtain a mixed solution B; centrifuging the mixed solution B to obtain the calcium sulfate ion oligomer.

[0034] Optionally, the centrifuging of the mixed solution B to obtain the calcium sulfate ion oligomer comprises: centrifuging the mixed solution B in a centrifuge at a speed of 4000 rpm, and washing the centrifuged polymer with ethanol to remove residual triethylamine to obtain the calcium sulfate ion oligomer.

[0035] Optionally, the mass fraction ratio of Ca and triethylamine in the mixed solution A is 1:5-1:50, and the mass fraction ratio of Ca and triethylamine determines the polymerization degree of the calcium sulfate ion oligomer. With the gradual increase of the proportion of triethylamine, the polymerization degree of the calcium sulfate ion oligomer gradually decreases.

[0036] In a possible implementation, in the mixed system solution, the total mass concentration of polyvinylidene fluoride and the calcium sulfate ion oligomer is 3%-7%, and the mass fraction of the calcium sulfate ion oligomer is 0.1%-1% of the polyvinylidene fluoride.

[0037] In a possible implementation, the mixed N,N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer comprises: mixing N,N-dimethylformamide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; and adding the calcium sulfate ion oligomer into the polyvinylidene fluoride solution and stirring to obtain a mixed system solution.

[0038] Optionally, the adding the calcium sulfate ion oligomer into the polyvinylidene fluoride solution and stirring comprises: adding the calcium sulfate ion oligomer into the polyvinylidene fluoride solution at 35-40°C and magnetically stirring uniformly at 1000-5000 r / min.

[0039] In a possible implementation, the solidifying the mixed system solution into a film comprises: dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven.

[0040] Optionally, the dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven comprises: dropping the mixed system solution onto a glass slide and solidifying into a film in a vacuum oven at 90-120°C.

[0041] In another embodiment of the present application, a polyvinylidene fluoride dielectric composite film is provided, in particular a polyvinylidene fluoride dielectric composite film doped with calcium sulfate ion oligomers, which is prepared by the above-mentioned method for preparing a polyvinylidene fluoride dielectric composite film.

[0042] In another embodiment of the present application, the above-mentioned polyvinylidene fluoride dielectric composite film is applied to the preparation of a high-temperature-resistant thermistor device. Based on the strong dielectric property of the polyvinylidene fluoride dielectric composite film doped with calcium sulfate ion oligomers, the overall performance of the thermistor device can be further improved.

[0043] The method for preparing a polyvinylidene fluoride dielectric composite film according to the present application is described below with specific examples.

[0044] Example 1

[0045] Step 1: A mixed system solution of polyvinylidene fluoride and calcium sulfate ionic oligomer with a total mass concentration of 3% was prepared using N,N-dimethylformamide as a solvent. The mass fraction of the calcium sulfate ionic oligomer was 0.1% of the polyvinylidene fluoride.

[0046] When preparing the mixed system solution, N,N-dimethylformamide and polyvinylidene fluoride were first mixed to obtain a polyvinylidene fluoride solution, and then the calcium sulfate ionic oligomer was added to the polyvinylidene fluoride solution at 36°C and uniformly stirred at 4000 r / min by magnetic stirring.

[0047] Step 2: The mixed system solution in Step 1 was dropped onto a glass slide, and a polyvinylidene fluoride dielectric composite film was obtained by curing into a film in a vacuum oven at 90°C.

[0048] In addition, the calcium sulfate ionic oligomer used in Example 1 was prepared in the following manner: triethylamine was added to an alcohol solution of CaCl2·2H2O and stirred to obtain a mixed solution A; H2SO4 alcohol solution was added to the mixed solution A and stirred to obtain a mixed solution B; the mixed solution B was centrifuged, and the centrifuged polymer was washed with ethanol to remove residual triethylamine to obtain the calcium sulfate ionic oligomer.

[0049] Example 1 was repeated 4 times, and the mass fraction ratios of Ca to triethylamine in the mixed solution A in the 4 times were 1:5, 1:15, 1:30 and 1:50, respectively.

[0050] Example 2

[0051] Step 1: A mixed system solution of polyvinylidene fluoride and calcium sulfate ionic oligomer with a total mass concentration of 4% was prepared using N,N-dimethylformamide as a solvent. The mass fraction of the calcium sulfate ionic oligomer was 0.3% of the polyvinylidene fluoride.

[0052] When preparing the mixed system solution, N,N-dimethylformamide and polyvinylidene fluoride were first mixed to obtain a polyvinylidene fluoride solution, and then the calcium sulfate ionic oligomer was added to the polyvinylidene fluoride solution at 40°C and uniformly stirred at 1000 r / min by magnetic stirring.

[0053] Step 2: The mixed system solution in Step 1 was dropped onto a glass slide, and a polyvinylidene fluoride dielectric composite film was obtained by curing into a film in a vacuum oven at 100°C.

[0054] In addition, the calcium sulfate ionic oligomer used in Example 2 is prepared in the following manner: triethylamine is added to an alcohol solution of CaCl2 2H2O and stirred to obtain a mixed solution A; an alcohol solution of H2SO4 is added to the mixed solution A and stirred to obtain a mixed solution B; the mixed solution B is centrifuged, and the centrifuged polymer is washed with ethanol to remove residual triethylamine to obtain the calcium sulfate ionic oligomer.

[0055] Example 2 is repeated 4 times, and the mass fraction ratio of Ca to triethylamine in the mixed solution A in the 4 times is 1:5, 1:15, 1:30 and 1:50, respectively.

[0056] Example 3

[0057] Step 1: A mixed system solution of polyvinylidene fluoride and calcium sulfate ionic oligomer with a total mass concentration of 5% is prepared using N,N-dimethylformamide as a solvent. The mass fraction of the calcium sulfate ionic oligomer is 0.5% of the polyvinylidene fluoride.

[0058] When preparing the mixed system solution, N,N-dimethylformamide and polyvinylidene fluoride are first mixed to obtain a polyvinylidene fluoride solution, and then the calcium sulfate ionic oligomer is added to the polyvinylidene fluoride solution at 40°C and uniformly stirred at 2000 r / min by magnetic stirring.

[0059] Step 2: The mixed system solution in Step 1 is dropped onto a glass slide, and a polyvinylidene fluoride dielectric composite film is obtained by curing into a film in a vacuum oven at 110°C.

[0060] In addition, the calcium sulfate ionic oligomer used in Example 3 is prepared in the following manner: triethylamine is added to an alcohol solution of CaCl2 2H2O and stirred to obtain a mixed solution A; an alcohol solution of H2SO4 is added to the mixed solution A and stirred to obtain a mixed solution B; the mixed solution B is centrifuged, and the centrifuged polymer is washed with ethanol to remove residual triethylamine to obtain the calcium sulfate ionic oligomer.

[0061] Example 3 is repeated 4 times, and the mass fraction ratio of Ca to triethylamine in the mixed solution A in the 4 times is 1:5, 1:15, 1:30 and 1:50, respectively.

[0062] Example 4

[0063] Step 1: A mixed system solution of polyvinylidene fluoride and calcium sulfate ionic oligomer with a total mass concentration of 6% is prepared using N,N-dimethylformamide as a solvent. The mass fraction of the calcium sulfate ionic oligomer is 0.7% of the polyvinylidene fluoride.

[0064] When the mixed system solution is prepared, the N,N-dimethylformamide and the polyvinylidene fluoride are mixed to obtain a polyvinylidene fluoride solution, and then the calcium sulfate ion oligomer is added into the polyvinylidene fluoride solution at 38°C and stirred uniformly at 4000 r / min by magnetic force.

[0065] Step 2: The mixed system solution in step 1 is dropped onto a glass slide, and cured into a film in a vacuum oven at 100°C to obtain a polyvinylidene fluoride dielectric composite film.

[0066] In addition, the calcium sulfate ion oligomer used in Example 4 is prepared in the following manner: triethylamine is added into an alcohol solution of CaCl2·2H2O and stirred to obtain a mixed solution A; an alcohol solution of H2SO4 is added into the mixed solution A and stirred to obtain a mixed solution B; the mixed solution B is centrifuged, and the centrifuged polymer is washed with ethanol to remove residual triethylamine to obtain the calcium sulfate ion oligomer.

[0067] Example 4 is repeated for 4 times, and the mass fraction ratio of Ca to triethylamine in the mixed solution A in the 4 times is 1:5, 1:15, 1:30 and 1:50, respectively.

[0068] Example 5

[0069] Step 1: A mixed system solution of polyvinylidene fluoride and calcium sulfate ion oligomer with a total mass concentration of 7% is prepared by using N,N-dimethylformamide as a solvent. The mass fraction of the calcium sulfate ion oligomer is 1% of the polyvinylidene fluoride.

[0070] When the mixed system solution is prepared, the N,N-dimethylformamide and the polyvinylidene fluoride are mixed to obtain a polyvinylidene fluoride solution, and then the calcium sulfate ion oligomer is added into the polyvinylidene fluoride solution at 35°C and stirred uniformly at 5000 r / min by magnetic force.

[0071] Step 2: The mixed system solution in step 1 is dropped onto a glass slide, and cured into a film in a vacuum oven at 120°C to obtain a polyvinylidene fluoride dielectric composite film.

[0072] In addition, the calcium sulfate ion oligomer used in Example 5 is prepared in the following manner: triethylamine is added into an alcohol solution of CaCl2·2H2O and stirred to obtain a mixed solution A; an alcohol solution of H2SO4 is added into the mixed solution A and stirred to obtain a mixed solution B; the mixed solution B is centrifuged, and the centrifuged polymer is washed with ethanol to remove residual triethylamine to obtain the calcium sulfate ion oligomer.

[0073] Example 5 is repeated for 4 times, and the mass fraction ratio of Ca to triethylamine in the mixed solution A in the 4 times is 1:5, 1:15, 1:30 and 1:50, respectively.

[0074] Example 6

[0075] Step 1: Using N,N-dimethylformamide as a solvent, prepare a mixed solution of polyvinylidene fluoride and calcium sulfate oligomers with a total mass concentration of 5%. The mass fraction of the calcium sulfate oligomers is 0.5% of the polyvinylidene fluoride.

[0076] When preparing the mixed system solution, N,N-dimethylformamide and polyvinylidene fluoride are first mixed to obtain a polyvinylidene fluoride solution. Then, calcium sulfate ion oligomers are added to the polyvinylidene fluoride solution at 40°C and magnetically stirred at 2000 r / min until homogeneous.

[0077] Step 2: Drop the mixed solution from Step 1 onto a glass slide and cure it in a vacuum oven at 110°C to obtain a polyvinylidene fluoride dielectric composite film.

[0078] The calcium sulfate ion oligomer used in Example 6 was prepared by adding an alcoholic solution of H2SO4 to an alcoholic solution of CaCl2·2H2O, stirring and centrifuging to obtain the calcium sulfate ion oligomer.

[0079] See Figure 1 Fourier transform infrared spectra of polyvinylidene fluoride dielectric composite films doped with calcium sulfate ion oligomers of different degrees of polymerization are shown. The mass fraction of calcium sulfate ion oligomers is 0.5% of polyvinylidene fluoride.

[0080] Wherein, P-Ca:TEA = 1:50 means that the mass fraction ratio of Ca to triethylamine in mixed solution A is 1:50; P-Ca:TEA = 1:30 means that the mass fraction ratio of Ca to triethylamine in mixed solution A is 1:30; P-Ca:TEA = 1:15 means that the mass fraction ratio of Ca to triethylamine in mixed solution A is 1:15; P-Ca:TEA = 1:5 means that the mass fraction ratio of Ca to triethylamine in mixed solution A is 1:5.

[0081] See Figure 2 The Fourier transform infrared spectra of polyvinylidene fluoride dielectric composite films doped with different amounts of calcium sulfate ion oligomers are shown. In the mixed solution A, the mass fraction ratio of Ca to triethylamine is 1:30.

[0082] P-1 means that the mass fraction of calcium sulfate ion oligomer is 1% of polyvinylidene fluoride; P-0.7 means that the mass fraction of calcium sulfate ion oligomer is 0.7% of polyvinylidene fluoride; P-0.5 means that the mass fraction of calcium sulfate ion oligomer is 0.5% of polyvinylidene fluoride; P-0.3 means that the mass fraction of calcium sulfate ion oligomer is 0.3% of polyvinylidene fluoride; P-0.1 means that the mass fraction of calcium sulfate ion oligomer is 0.1% of polyvinylidene fluoride; PVDF means polyvinylidene fluoride film without doping.

[0083] In combination Figure 1 and 2 It can be seen that both β and γ polar crystal forms are generated in the mixed system of polyvinylidene fluoride and calcium sulfate ion oligomer.

[0084] Referring to Figure 3 and 4 , the dielectric constant and dielectric loss of polyvinylidene fluoride dielectric composite films doped with calcium sulfate ion oligomers of different polymerization degrees are shown. Among them, P-CaSO4 represents the polyvinylidene fluoride dielectric composite film prepared in Example 6. It can be seen that as the proportion of triethylamine increases, the polymerization degree of calcium sulfate ion oligomer decreases, and the dielectric constant of the polyvinylidene fluoride dielectric composite film also increases. When the mass fraction ratio of Ca and triethylamine in the mixed solution A is 1:30, the dielectric constant of the polyvinylidene fluoride dielectric composite film is 23.95, which is 2.4 times that of the pure polyvinylidene fluoride film, and the dielectric constant does not increase significantly.

[0085] Referring to Figure 5 and 6 , the dielectric constant and dielectric loss of polyvinylidene fluoride dielectric composite films doped with different amounts of calcium sulfate ion oligomers are shown. It can be seen that as the amount of calcium sulfate ion oligomer added increases, the dielectric constant also increases. At 1 kHz, the dielectric constant of P-1 increases to 30.69, which is 3 times that of the pure polyvinylidene fluoride film. Similarly, as the amount of addition increases, the dielectric loss does not increase significantly, but when the amount of addition increases by 1%, it can be seen that at 100 Hz, the dielectric loss increases slightly, which may be due to excessive crosslinking caused by excessive addition, resulting in an increase in dielectric loss.

[0086] Referring to Figure 7The UV-Vis transmittance spectra of pure PVDF, PVDF / CaSO4 ion oligomer and PVDF / CaSO4 composite films are shown. The transmittance of pure PVDF film in the visible region is 73%, and the transmittance of the composite film after adding CaSO4 powder increases to only 81%, which may be due to the decrease of the grain size. The addition of CaSO4 ion oligomer significantly improves the transmittance of the film, up to 90%. This is because the addition of CaSO4 ion oligomer reduces the crystallinity of the composite film and reduces its scattering of visible light.

[0087] It is found through detection and comparison that in the polyvinyl fluoride dielectric composite film added with CaSO4 ion oligomer, the dielectric constant of the polyvinyl fluoride dielectric composite film is significantly increased, the dielectric loss is not significantly increased, and the energy storage performance is significantly improved. The prepared polyvinyl fluoride dielectric composite film can replace traditional ceramic dielectric materials, and the preparation method is simple, easy to operate and convenient to popularize.

[0088] The above content only illustrates the technical idea of the present application and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the claims of the present application.

Claims

1. A method for preparing a polyvinylidene fluoride dielectric composite film, characterized by, The method comprises the following steps: mixing N,N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer to obtain a mixed system solution; and curing the mixed system solution into a film to obtain a polyvinylidene fluoride dielectric composite film. The method further comprises the following steps: adding triethylamine to an alcohol solution of CaCl2·2H2O and stirring to obtain a mixed solution A; adding an alcohol solution of H2SO4 to the mixed solution A and stirring to obtain a mixed solution B; centrifuging the mixed solution B, and washing the centrifuged polymer with ethanol to remove residual triethylamine to obtain calcium sulfate ion oligomer; the mass fraction ratio of Ca to triethylamine in the mixed solution A is 1:5-1:50; in the mixed system solution, the mass fraction of calcium sulfate ion oligomer is 0.1%-1% of polyvinylidene fluoride.

2. The method for preparing polyvinylidene fluoride dielectric composite film according to claim 1, characterized in that, in the mixed system solution, the total mass concentration of polyvinylidene fluoride and calcium sulfate ion oligomer is 3%-7%.

3. The method for preparing polyvinylidene fluoride dielectric composite film according to claim 1, characterized in that, The mixing of N,N-dimethylformamide, polyvinylidene fluoride and calcium sulfate ion oligomer comprises the following steps: mixing N,N-dimethylformamide and polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; adding calcium sulfate ion oligomer to the polyvinylidene fluoride solution and stirring to obtain a mixed system solution.

4. The method for preparing polyvinylidene fluoride dielectric composite film according to claim 3, characterized in that, The step of adding calcium sulfate ion oligomer to the polyvinylidene fluoride solution and stirring comprises the following steps: adding calcium sulfate ion oligomer to the polyvinylidene fluoride solution at 35-40℃ and stirring uniformly at 1000-5000r / min by magnetic stirring.

5. The method for preparing polyvinylidene fluoride dielectric composite film according to claim 1, characterized in that, The step of curing the mixed system solution into a film comprises the following steps: dropping the mixed system solution onto a glass slide and curing into a film in a vacuum oven.

6. The method for preparing polyvinylidene fluoride dielectric composite film according to claim 1, characterized in that, The step of dropping the mixed system solution onto a glass slide and curing into a film in a vacuum oven comprises the following steps: dropping the mixed system solution onto a glass slide and curing into a film in a vacuum oven at 90-120℃.

7. A polyvinylidene fluoride dielectric composite film, characterized by, The polyvinylidene fluoride dielectric composite film is prepared by the method for preparing a polyvinylidene fluoride dielectric composite film according to any one of claims 1-6.

8. Use of the polyvinylidene fluoride dielectric composite film according to claim 7 in the preparation of a high-temperature-resistant thermistor device.

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