PVDF (Polyvinylidene Fluoride)-based composite dielectric film based on laminated structure as well as preparation and application of PVDF-based composite dielectric film

Abstract

The invention relates to the technical field of polymer composite film processing, in particular to a PVDF-based composite dielectric film based on a laminated structure and preparation and application of the PVDF-based composite dielectric film. Aiming at the requirement of an efficient energy storage polyvinylidene fluoride (PVDF)-based dielectric film and aiming at reducing dielectric loss and improving charging and discharging efficiency, a blending layer with a micro-phase separation structure is constructed by introducing low-loss and high-insulation linear dielectric polyetherimide (PEI) with different proportions into PVDF, and laminated hot-pressing assembly is carried out. Compared with a traditional method of introducing an inorganic filler, the preparation method provided by the invention selects an all-organic system, utilizes a preparation method of simple physical blending, coating film formation and then lamination hot-pressing assembly, fully combines respective advantages of a ferroelectric polymer and a linear polymer, and avoids the problem of serious reduction of mechanical properties caused by filler aggregation.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer composite film processing, in particular to a PVDF-based composite dielectric film based on a laminated structure and the preparation and application thereof. Background Art

[0002] With the rapid development of new energy power generation, electric vehicles, and pulse power equipment, dielectric capacitors have become an indispensable core energy storage component in electronic systems due to their high power density and fast charging and discharging characteristics. Polymer-based capacitors are considered to be a new generation of capacitor materials due to their excellent breakdown strength, extremely low dielectric loss, flexibility, and easy processing. However, the energy density of existing commercial polymer dielectrics is low and it is difficult to meet the miniaturization requirements of high-energy-density devices. For example, the most widely used biaxially oriented polypropylene (BOPP) film has a breakdown strength of up to 700MV / m, but its energy storage density is only 2J / cm 3 , at least one order of magnitude lower than traditional chemical batteries, which not only limits the miniaturization and lightweighting of electronic components, but also increases the design cost and difficulty. Although the dielectric constant of the composite material can be improved by introducing inorganic ceramic fillers (such as barium titanate, strontium titanate, etc.), the poor interface compatibility between the inorganic filler and the organic matrix and the uneven dispersion of the filler can easily cause local electric field distortion, resulting in a significant reduction in breakdown strength and limited improvement in energy storage performance. In addition, a high content of inorganic fillers in traditional blended composite materials will significantly deteriorate the flexibility and processing properties of the material. Against this background, the preparation of all-organic dielectric films with both excellent discharge energy storage density and high breakdown strength for use in the field of dielectric energy storage remains a major challenge. Summary of the Invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide a PVDF-based composite dielectric film based on a laminated structure and its preparation and application.

[0004] The purpose of the present invention can be achieved by the following technical solutions:

[0005] The first object of the present invention is to provide a PVDF-based composite dielectric film based on a laminated structure, comprising a PVDF layer and a PVDF / PEI mixed film laminated on both sides of the PVDF film;

[0006] One or more PVDF / PEI mixed membranes are arranged on each side of the PVDF membrane.

[0007] In one embodiment of the present invention, one or two sets of PVDF / PEI mixed membranes are provided on each side of the PVDF membrane;

[0008] The thickness of the PVDF membrane is 10 to 12 μm, and the thickness of the single-layer PVDF / PEI mixed membrane is 10 to 12 μm.

[0009] In one embodiment of the present invention, the mass ratio of PVDF to PEI in the PVDF / PEI mixed membrane is 9:1 to 8:2 (preferably, the mass ratio of PVDF to PEI is 9:1 or 8:2).

[0010] A second object of the present invention is to provide a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0011] (S1) dissolving PVDF to obtain a PVDF solution, and sequentially subjecting the PVDF solution to doctor coating (e.g., doctor coating using a 120 μm coating rod), solvent removal, high-temperature quenching, and drying to obtain a PVDF membrane;

[0012] (S2) dissolving PEI and adding PVDF, mixing to obtain a mixed solution; sequentially subjecting the mixed solution to doctor blade coating, solvent removal, high-temperature quenching, and drying to obtain a first PVDF / PEI membrane;

[0013] (S3) adjusting the amounts of PEI and PVDF, and repeating step (S2) to obtain a second PVDF / PEI membrane;

[0014] (S4) stacking the membrane layers prepared in step (S2) and step (S3) on both sides of the PVDF membrane prepared in step (S1), hot pressing and quenching, and finally drying to obtain a PVDF-based composite dielectric film based on a laminated structure.

[0015] In one embodiment of the present invention, in step (S1), the PVDF is selected from one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer or poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer (preferably, the PVDF is polyvinylidene fluoride);

[0016] The concentration of the PVDF solution is 8-12 wt % (preferably, the concentration of the PVDF solution is 10 wt %).

[0017] In one embodiment of the present invention, PVDF is dissolved in NMP.

[0018] In one embodiment of the present invention, in step (S1), the temperature during the solvent removal treatment is 60 to 80° C. and the time is 10 to 15 hours (preferably, the temperature during the solvent removal treatment is 80° C. and the time is 12 hours);

[0019] During the high-temperature quenching treatment, the temperature is 180-200°C for 5-10 minutes, and then immediately quenched in ice water (preferably, during the high-temperature quenching treatment, the temperature is 200°C for 6 minutes);

[0020] During the drying process, the temperature is 50-70° C. and the time is 10-14 h (preferably, during the drying process, the temperature is 60° C. and the time is 12 h).

[0021] In one embodiment of the present invention, in step (S2), the concentration of PVDF in the mixed solution is 6-9 wt%, and the concentration of PEI is 1-4 wt%;

[0022] During the solvent removal process, the temperature is 60-80° C. and the time is 10-15 hours (preferably, during the solvent removal process, the temperature is 80° C. and the time is 12 hours);

[0023] During the high temperature quenching treatment, the temperature is 180-200°C and the time is 5-10 minutes; (Preferably, during the high temperature quenching treatment, the temperature is 200°C and the time is 6 minutes)

[0024] During the drying process, the temperature is 60-80°C and the time is 10-15 hours. (Preferably, during the drying process, the temperature is 60°C and the time is 12 hours)

[0025] In one embodiment of the present invention, PEI is dissolved in NMP.

[0026] In one embodiment of the present invention, in step (S4), during the hot pressing process, the pressure is 10-15 MPa, the temperature is 180-200°C, and the time is 5-10 min (preferably, during the hot pressing process, the pressure is 15 MPa, the temperature is 200°C, and the time is 6 min).

[0027] In one embodiment of the present invention, in step (S4), during the drying process, the temperature is 60-80°C and the time is 10-15 hours (preferably, during the drying process, the temperature is 60°C and the time is 12 hours).

[0028] In one embodiment of the present invention, the stacking design concept of the multilayer film is based on symmetrical gradient and asymmetrical gradient, and the number of layers is three or five; the stacking order is three layers of symmetry, three layers of asymmetric gradient, five layers of symmetrical gradient, etc.; the multilayer composite film is named with the symbol "-".

[0029] The third object of the present invention is to provide a PVDF-based composite dielectric film based on a laminated structure for use in a high-pulse power system.

[0030] To address the high remanent polarization strength, dielectric loss, and low charge-discharge efficiency of existing ferroelectric polymers, such as polyvinylidene fluoride (PVDF) and its copolymers, methods were explored to suppress the polarization strength of PVDF. A multiphase film was formed by combining it with polyetherimide (PEI) in varying proportions. Through a layered design, the rapidly increasing dielectric loss and conductivity under high electric fields were mitigated, thereby enhancing the energy storage properties of PVDF. PEI, as a linear dielectric component, forms a uniform microphase structure with the ferroelectric polymer PVDF matrix. Leveraging the inherent low dielectric loss and high breakdown strength of the linear dielectric, combined with the micro-interfaces between phases and the macro-interfaces between layers, the overall energy storage properties of the composite dielectric film were enhanced.

[0031] The technical solution principle of the present invention is as follows:

[0032] The microphase structure is presented by the blend system of ferroelectric polymer PVDF and linear dielectric PEI. The existence of continuous microphase makes the PVDF-based composite film have both high strength and high toughness. The excellent mechanical properties provide higher breakdown strength. At the same time, the linear characteristics of PEI limit the dipole motion of the composite film at high frequencies, effectively reducing residual polarization and suppressing dielectric loss. Furthermore, the multilayer structure design introduces interlayer interfaces, and uses the differences in dielectric constants of each layer to construct a carrier barrier, extend the breakdown path, and improve dielectric performance.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The preparation process of the PVDF-based composite dielectric film based on a laminated structure provided by the present invention is simple and the raw materials are readily available;

[0035] (2) The PVDF-based composite dielectric film based on a laminated structure prepared by the present invention reduces the dielectric loss of the material while maintaining high dielectric properties due to its reasonable structural design;

[0036] (3) The PVDF-based composite dielectric film based on a laminated structure prepared by the present invention improves the mechanical strength of the film while improving the energy storage density due to its reasonable structural design. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The stress-strain curves of the composite films prepared in Examples 1 to 2 and Comparative Examples 1 to 4 are shown;

[0038] Figure 2 The relative dielectric constant and dielectric loss diagram of the composite films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 and Comparative Examples 7 to 8;

[0039] Figure 3Hysteresis loops of the composite films prepared for Examples 1 to 3 and Comparative Examples 7 to 8 under breakdown field strength;

[0040] Figure 4 The hysteresis loops of the composite films prepared in Comparative Examples 1 to 4 under breakdown field strength are shown. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] In the following examples, unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0043] Example 1

[0044] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0045] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0046] (S2) Preparation of PVDF / PEI composite membrane: 0.2 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.8 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate completely. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 9 / 1.

[0047] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 9 / 1 prepared in step (S2) is used as the upper and lower layers. The membrane is then stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then drying in a 60°C oven for 12 hours to obtain a three-layer symmetrical 9 / 1-PVDF-9 / 1 composite membrane.

[0048] Example 2

[0049] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0050] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0051] (S2) Preparation of PVDF / PEI composite membrane: 0.4 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.6 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was placed in an 80°C oven for 12 h to allow the solvent to evaporate completely. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 8 / 2.

[0052] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 8 / 2 prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then placing in a 60°C oven for 12 hours to completely dry, thereby obtaining a three-layer symmetrical 8 / 2-PVDF-8 / 2 composite membrane.

[0053] Example 3

[0054] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0055] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0056] (S2) Preparation of PVDF / PEI composite membrane:

[0057] 0.2 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h at room temperature. 1.8 g of PVDF was then added to the system and stirred for another 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod and placed in an 80°C oven for 12 h to fully evaporate the solvent. The film was then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was named composite membrane 9 / 1.

[0058] 0.4 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h at room temperature. 1.6 g of PVDF was then added to the system and stirred for another 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod and placed in an 80°C oven for 12 h to fully evaporate the solvent. The film was then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was named composite membrane 8 / 2.

[0059] (S3) The PVDF membrane prepared in step (S1) and the composite membranes 9 / 1 and 8 / 2 prepared in step (S2) are stacked, with the following from top to bottom: composite membrane 8 / 2, composite membrane 9 / 1, PVDF, composite membrane 9 / 1, and composite membrane 8 / 2, respectively. The laminated structure is hot pressed and quenched to obtain a PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then placing in a 60°C oven for 12 hours to completely dry, to obtain a five-layer symmetrical gradient 8 / 2-9 / 1-PVDF-9 / 1-8 / 2 composite membrane.

[0060] Example 4

[0061] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0062] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was placed in an oven at 60°C for 15 h to allow the solvent to evaporate completely. The solution was then placed at 220°C for 6 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in an oven at 50°C for 14 h to obtain a PVDF membrane.

[0063] (S2) Preparation of PVDF / PEI composite membrane: 0.4 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.6 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The membrane was then placed in an oven at 70°C for 10 h to allow the solvent to evaporate completely. The membrane was then placed at 180°C for 10 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in an oven at 70°C for 10 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 8 / 2.

[0064] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 8 / 2 prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 180°C and 12 MPa for 10 minutes, followed by quenching in ice water, and then placing in a 70°C oven for 15 hours to completely dry, thereby obtaining a three-layer symmetrical 8 / 2-PVDF-8 / 2 composite membrane.

[0065] Example 5

[0066] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0067] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was placed in an oven at 60°C for 15 h to allow the solvent to evaporate completely. The solution was then placed at 220°C for 6 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in an oven at 50°C for 14 h to obtain a PVDF membrane.

[0068] (S2) Preparation of PVDF / PEI composite membrane: 0.4 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.6 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate completely. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 14 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, the composite membrane was designated as 8 / 2.

[0069] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 8 / 2 prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 190°C and 10 MPa for 5 minutes, followed by quenching in ice water, and then placing in an 80°C oven for 10 hours to completely dry, thereby obtaining a three-layer symmetrical 8 / 2-PVDF-8 / 2 composite membrane.

[0070] Example 6

[0071] This embodiment provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0072] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was placed in an oven at 60°C for 15 h to allow the solvent to evaporate completely. The solution was then placed at 220°C for 6 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in an oven at 50°C for 14 h to obtain a PVDF membrane.

[0073] (S2) Preparation of PVDF / PEI composite membrane: 0.4 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.6 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The membrane was then placed in an oven at 60°C for 12 h to allow the solvent to evaporate completely. The membrane was then placed at 220°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in an oven at 70°C for 14 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 8 / 2.

[0074] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 8 / 2 prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 12 MPa for 10 minutes, followed by quenching in ice water, and then placing in a 70°C oven for 15 hours to completely dry, thereby obtaining a three-layer symmetrical 8 / 2-PVDF-8 / 2 composite membrane.

[0075] Comparative Example 1

[0076] A dielectric film provided in this comparative example is prepared by the following method:

[0077] (S1) 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm for 12 h at room temperature until fully dissolved to obtain a uniform solution;

[0078] (S2) The solution was coated onto a glass plate using a 120 μm coating rod, placed in an 80°C oven for 12 h to allow the solvent to fully evaporate, then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a dielectric film: PVDF membrane.

[0079] Comparative Example 2

[0080] A dielectric film provided in this comparative example is prepared by the following method:

[0081] (S1) 2 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 12 h at room temperature until fully dissolved to obtain a homogeneous solution;

[0082] (S2) The solution was coated onto a glass plate using a 120 μm coating rod, placed in an 80°C oven for 12 h to allow the solvent to fully evaporate, then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a dielectric film: PEI film.

[0083] Comparative Example 3

[0084] A dielectric film provided in this comparative example is prepared by the following method:

[0085] (S1) 0.2 g of PEI was added to 18 g of NMP and stirred at 600 rpm at room temperature for 6 h. 1.8 g of PVDF was then added and stirred for another 12 h until fully dissolved to obtain a uniform solution.

[0086] (S2) The solution was coated onto a glass plate using a 120 μm coating rod, placed in an 80°C oven for 12 h to allow the solvent to fully evaporate, then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a composite dielectric film: composite film 9 / 1.

[0087] Comparative Example 4

[0088] A dielectric film provided in this comparative example is prepared by the following method:

[0089] (S1) 0.4 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h. 1.6 g of PVDF was then added and stirred for another 12 h until fully dissolved to obtain a uniform solution.

[0090] (S2) The solution was coated onto a glass plate using a 120 μm coating rod, placed in an 80°C oven for 12 h to allow the solvent to fully evaporate, then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a composite dielectric film: composite film 8 / 2.

[0091] Comparative Example 5

[0092] A dielectric film provided in this comparative example is prepared by the following method:

[0093] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0094] (S2) Preparation of PVDF / PEI composite membrane: 0.6 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.4 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate completely. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 7 / 3.

[0095] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the composite membrane 7 / 3 prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then placing in a 60°C oven for 12 hours to completely dry, thereby obtaining a three-layer symmetrical 7 / 3-PVDF-7 / 3 composite membrane.

[0096] Comparative Example 6

[0097] A dielectric film provided in this comparative example is prepared by the following method:

[0098] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0099] (S2) Preparation of PVDF / PEI composite membrane: 0.8 g PEI was added to 18 g NMP and stirred at 600 rpm at room temperature for 6 h. 1.2 g PVDF was then added to the system and stirred for an additional 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate completely. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was designated as composite membrane 6 / 4.

[0100] (S3) The PVDF membrane prepared in step (S1) above is used as the middle layer, and the 6 / 4 composite membrane prepared in step (S2) is used as the upper and lower layers, and the membrane is stacked, hot pressed, and quenched to obtain a laminated PVDF-based composite dielectric film. The hot pressing conditions are as follows: hot pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then placing in a 60°C oven for 12 hours to completely dry, thereby obtaining a three-layer symmetrical 6 / 4-PVDF-6 / 4 composite membrane.

[0101] Comparative Example 7

[0102] This comparative example provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0103] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0104] (S2) Preparation of PVDF / PEI composite membrane:

[0105] 0.4 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h at room temperature. 1.6 g of PVDF was then added to the system and stirred for another 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod and placed in an 80°C oven for 12 h to fully evaporate the solvent. The film was then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was named composite membrane 8 / 2.

[0106] (S3) The PVDF membrane prepared in step (S1) and the composite membrane 8 / 2 prepared in step (S2) are laminated, with PVDF, composite membrane 8 / 2, and PVDF being laminated from top to bottom, respectively. The laminated membrane is then hot-pressed and quenched to obtain a laminated PVDF-based composite dielectric film. The hot-pressing conditions are as follows: hot-pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then drying in a 60°C oven for 12 hours to obtain a three-layer symmetrical PVDF-8 / 2-PVDF composite membrane.

[0107] Comparative Example 8

[0108] This comparative example provides a method for preparing a PVDF-based composite dielectric film based on a laminated structure, comprising the following steps:

[0109] (S1) Preparation of PVDF membrane: 2 g of PVDF was added to 18 g of NMP and stirred at 600 rpm at room temperature for 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod. The solution was then placed in an 80°C oven for 12 h to allow the solvent to evaporate. The solution was then placed at 200°C for 5 min and immediately quenched in ice water. The membrane was removed from the glass plate and dried in a 60°C oven for 12 h to obtain a PVDF membrane.

[0110] (S2) Preparation of PVDF / PEI composite membrane:

[0111] 0.2 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h at room temperature. 1.8 g of PVDF was then added to the system and stirred for another 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod and placed in an 80°C oven for 12 h to fully evaporate the solvent. The film was then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was named composite membrane 9 / 1.

[0112] 0.4 g of PEI was added to 18 g of NMP and stirred at 600 rpm for 6 h at room temperature. 1.6 g of PVDF was then added to the system and stirred for another 12 h until fully dissolved to obtain a uniform solution. The solution was then spread onto a glass plate using a 120 μm coating rod and placed in an 80°C oven for 12 h to fully evaporate the solvent. The film was then placed at 200°C for 5 min and immediately quenched in ice water. The film was removed from the glass plate and placed in a 60°C oven for 12 h to fully dry to obtain a PVDF / PEI composite membrane. Based on the mass ratio of PVDF to PEI, it was named composite membrane 8 / 2.

[0113] (S3) The PVDF membrane prepared in step (S1) and the composite membranes 9 / 1 and 8 / 2 prepared in step (S2) are laminated, with the composite membrane 8 / 2, the composite membrane 9 / 1, and the PVDF being laminated from top to bottom, respectively. The laminated membranes are then hot-pressed and quenched to obtain a laminated PVDF-based composite dielectric film. The hot-pressing conditions are as follows: hot-pressing at 200°C and 15 MPa for 6 minutes, followed by quenching in ice water, and then drying in a 60°C oven for 12 hours to obtain a three-layer asymmetric gradient 8 / 2-9 / 1-PVDF composite membrane.

[0114] Performance Analysis:

[0115] Figure 1 The stress-strain curves of the composite films prepared in Examples 1 to 2 and Comparative Examples 1 to 4 are shown in Table 1. The tensile strength and elongation at break of the composite films prepared in Examples 1 to 3 and Comparative Examples 1 to 8 are summarized in Table 1. As can be seen from the data in Table 1, as the proportion of PEI increases, the tensile strength of the single-layer composite films of Comparative Examples 3 and 4 increases and the elongation at break decreases compared to Comparative Example 1. After hot pressing treatment, each single-layer film is laminated with different structures. The tensile strengths of the composite films prepared in Examples 1 and 2 are 24.1 MPa and 27.1 MPa, respectively, and the elongations at break are 75.8% and 52.2%, respectively. The above results show that the introduction of PEI into PVDF to prepare composite films with different proportions and different laminated structures has an inherent high tensile strength that enhances the mechanical properties of the composite system. The laminated hot pressing treatment allows each layer to be tightly combined, fully combining the advantages of each layer, while improving the toughness of the composite film while maintaining a certain flexibility.

[0116] Table 1 Summary of mechanical properties of Examples 1 to 5 and Comparative Examples 1 to 6

[0117]

[0118] Figure 2 The relative dielectric constant diagram of the composite films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 and Comparative Examples 7 to 8 is shown. Figure 2 It can be seen that in 10 2 ~10 6In the range of Hz, the dielectric constants of Examples 1 to 3 are all higher than those of Comparative Examples 1 and 2, among which the dielectric constants of Examples 1 and 2 based on the three-layer symmetrical structure design are higher than those of Comparative Examples 1 and 2. 3 Hz is 13.51 and 11.35, and the dielectric constant of comparative example 8 based on asymmetric structure design is between 10 3 Hz reached 15.02, and the dielectric constant of Example 3 based on the five-layer symmetrical gradient structure design was 10 3 Hz is 15.01. Considering the multi-layer design concept, the introduction of multiple heterogeneous interfaces can significantly improve the dielectric constant of the composite film, and the introduction of linear dielectric PEI can improve the frequency stability of the dielectric constant to a certain extent by virtue of its low dielectric loss characteristics. 3 The dielectric constants at Hz are 9.24, 7.69, 10.87, and 9.31 respectively.

[0119] Figure 3 The hysteresis loops of the composite films prepared in Examples 1 to 3 and Comparative Examples 7 to 8 under the breakdown field strength are shown in FIG. Figure 4 It can be seen that the breakdown strengths of Examples 1 to 3 and Comparative Examples 7 to 8 are 296.9KV / mm, 299.6KV / mm, 233.6KV / mm, 148.7KV / mm and 149.3KV / mm respectively. Among them, Example 2 with a three-layer symmetrical structure has the highest breakdown strength of 299.6KV / mm and the highest polarization of 4.57μC / cm 2 And reached 6.28J / cm 3 The optimal energy storage density is 3.30 J / cm 3 (Example 1), 4.98 J / cm 3 (Example 3), 3.51 J / cm 3 (Comparative Example 7), 2.21 J / cm 3 (Comparative Example 8), the calculation results highlight the superiority of this structural design. In addition, the maximum polarization under the breakdown field strength of Examples 1 to 3 is higher than that of Comparative Examples 1 to 8. This is not only due to the contribution of the interfacial polarization in the multilayer structure, but also the existence of the microphase structure in the PEI and PVDF composite system.

[0120] Figure 4 The hysteresis loops of the composite films prepared in Comparative Examples 1 to 4 under breakdown field strength are shown in FIG. Figure 3It can be seen that with the increase in the proportion of PEI in the single-layer composite membrane, the breakdown strength of Comparative Examples 3 and 4 increases, from 249.6KV / mm in Comparative Example 1 to 297.1KV / mm and 346.2KV / mm, which are all greater than the breakdown strength of 249.6KV / mm of the pure PVDF membrane in Comparative Example 1, and the hysteresis loop also becomes relatively slender, which corresponds to the reduction of energy loss and the improvement of energy storage efficiency during the charging and discharging process. In addition, due to the gradual increase in phase separation size, the compatibility of Comparative Examples 5 and 6 deteriorates, and the breakdown strength is 148.5KV / mm and 125.4KV / mm, respectively. According to the calculation formula of energy storage density and energy storage efficiency of dielectric materials, the improvement of breakdown strength is very beneficial to the increase of energy storage density. It is calculated that the energy storage density of Comparative Examples 1 to 6 is 2.99J / cm 3 , 2.36J / cm 3 , 2.02J / cm 3 , 3.10J / cm 3 , 1.34J / cm 3 , 0.65J / cm 3 , the energy storage efficiency increased from 70.3% in Comparative Example 1 to 83.3% in Comparative Example 3 and 84.1% in Comparative Example 4.

[0121] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the explanations of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A PVDF-based composite dielectric film based on a laminated structure, characterized in that: It includes a PVDF layer and a PVDF / PEI mixed membrane stacked on both sides of the PVDF membrane; One or more PVDF / PEI mixed membranes are arranged on each side of the PVDF membrane.

2. The PVDF-based composite dielectric film based on a laminated structure according to claim 1, characterized in that: One or two groups of PVDF / PEI mixed membranes are set on each side of the PVDF membrane; The thickness of the PVDF membrane is 10 to 12 μm, and the thickness of the single-layer PVDF / PEI mixed membrane is 10 to 12 μm.

3. The PVDF-based composite dielectric film based on a laminated structure according to claim 1, characterized in that: The mass ratio of PVDF to PEI in the PVDF / PEI mixed membrane is 9:1 to 8:

2.

4. A method for preparing a PVDF-based composite dielectric film with a laminated structure according to any one of claims 1 to 3, characterized in that: The following steps are involved: (S1) dissolving PVDF to obtain a PVDF solution, and sequentially subjecting the PVDF solution to doctor blade coating, solvent removal, high-temperature quenching, and drying to obtain a PVDF membrane; (S2) dissolving PEI and adding PVDF, mixing to obtain a mixed solution; sequentially subjecting the mixed solution to doctor blade coating, solvent removal, high-temperature quenching, and drying to obtain a first PVDF / PEI membrane; (S3) adjusting the amounts of PEI and PVDF, and repeating step (S2) to obtain a second PVDF / PEI membrane; (S4) stacking the membrane layers prepared in step (S2) and step (S3) on both sides of the PVDF membrane prepared in step (S1), hot pressing and quenching, and finally drying to obtain a PVDF-based composite dielectric film based on a laminated structure.

5. The method for preparing a PVDF-based composite dielectric film based on a laminated structure according to claim 4, characterized in that: In step (S1), the PVDF is selected from one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer or poly(vinylidene fluoride-chlorotrifluoroethylene) copolymer; The concentration of the PVDF solution is 8-12 wt%.

6. The method for preparing a PVDF-based composite dielectric film based on a laminated structure according to claim 4, characterized in that: In step (S1), during the solvent removal process, the temperature is 60-80°C and the time is 10-15 hours; During the high temperature quenching treatment, the temperature is 180-220°C for 5-10 minutes, and then immediately quenched in ice water; During the drying process, the temperature is 50-70°C and the time is 10-14 hours.

7. The method for preparing a PVDF-based composite dielectric film based on a laminated structure according to claim 4, characterized in that: In step (S2), the concentration of PVDF in the mixed solution is 6-9 wt%, and the concentration of PEI is 1-4 wt%; During the solvent removal process, the temperature is 60-80°C and the time is 10-15 hours; During the high temperature quenching treatment, the temperature is 180-220°C for 5-10 minutes, and then immediately quenched in ice water; During the drying process, the temperature is 60-80°C and the time is 10-15 hours.

8. The method for preparing a PVDF-based composite dielectric film based on a laminated structure according to claim 4, characterized in that: In step (S4), during the hot pressing process, the pressure is 10-15 MPa, the temperature is 180-200° C., and the time is 5-10 minutes.

9. The method for preparing a PVDF-based composite dielectric film based on a laminated structure according to claim 4, characterized in that: In step (S4), during the drying process, the temperature is 60 to 80° C. and the time is 10 to 15 hours.

10. Use of the PVDF-based composite dielectric film with a laminated structure according to any one of claims 1 to 3 in a high-pulse power system.

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