High-insulation COC capacitor film and preparation method and application thereof

Abstract

The invention discloses a high-insulation COC capacitor film and a preparation method and application thereof, and belongs to the technical field of energy storage dielectric materials and preparation thereof. The problems that under the existing high-temperature or high-electric-field condition, due to the fact that an interface Schottky barrier is reduced, carrier injection is aggravated, the conductivity loss of a COC dielectric thin film capacitor is sharply increased, the insulating performance is degraded, and the energy storage efficiency is reduced are solved. The method comprises the following steps: firstly, inducing an initiator to generate activated sites on the surface of a COC capacitance film by utilizing an ultraviolet light effect, and then carrying out grafting reaction between strong electron-deficient small organic molecules and electron-donating small organic molecules and the activated sites on the surface of the COC through ultraviolet induction; and a charge transfer complex is further formed on the surface of the COC film by utilizing the association effect of the two, so that the high-insulation COC capacitor film with the surface grafted with the charge transfer complex is obtained. The high-insulation COC capacitor film has excellent high-temperature energy storage performance and can be used for an energy storage device under the condition of electrothermal field coupling.

Description

Technical Field

[0001] The present invention relates to a highly insulating COC capacitive film and its preparation method and application, belonging to the technical field of energy storage dielectric materials and their preparation. Background Art

[0002] With the iterative upgrade of equipment towards high frequency, high power, and miniaturization, capacitors, as the core energy storage components of cutting-edge equipment such as new energy vehicle drive systems, electromagnetic launch devices, and high-energy weapons, are facing unprecedented performance challenges. Currently, the system working conditions have evolved from conventional steady-state operation to unsteady pulse working modes in extreme electrothermal coupling environments, which pose extremely high requirements for the energy storage stability and reliability of capacitors during long-term use. However, existing energy storage materials perform poorly in high electric fields, high temperatures, and complex electrothermal coupling environments, becoming a bottleneck restricting the wide application of energy storage capacitors.

[0003] The rigid structure of cycloolefin copolymer (COC) itself endows it with high thermal stability, low dielectric loss, and wide bandgap characteristics, making it a potential polymer material for developing high-temperature capacitors, meeting the requirements for dielectric capacitors at the present stage. However, the Schottky barrier at the electrode-dielectric interface decreases significantly under high temperature and high electric fields, resulting in increased carrier injection at the metal electrode, leading to a sharp increase in the conductance loss of the COC capacitive film, deterioration of insulation performance, and reduction of energy storage efficiency. However, current modification methods mainly focus on suppressing carrier migration in the COC body, and there is a lack of solutions for regulating carrier injection at the electrode. Therefore, it is very necessary to develop a dielectric material with high insulation characteristics and excellent energy storage efficiency by starting from improving the height of the interfacial Schottky barrier to suppress carrier injection at the electrode. Summary of the Invention

[0004] The present invention aims to solve the problems of sharp increase in conductance loss, deterioration of insulation performance, and reduction of energy storage efficiency of COC dielectric thin-film capacitors caused by the decrease of the interfacial Schottky barrier and the resulting increase in carrier injection under existing high-temperature or high-electric-field conditions, and provides a highly insulating COC capacitive film and its preparation method and application.

[0005] Technical Solution of the Present Invention:

[0006] One of the objectives of the present invention is to provide a preparation method of a highly insulating COC capacitive film, which includes the following steps:

[0007] (1) Clean and dry the COC film, place it in a photoinitiator solution, and perform surface irradiation pretreatment under a far-ultraviolet light source in a protective atmosphere to obtain a surface-activated COC film;

[0008] (2) Immerse the surface-activated COC film in a reaction solution containing strong electron-deficient organic small molecule substances and electron-donating organic small molecule substances, and place it under a far-ultraviolet light source in a protective atmosphere for irradiation grafting treatment. After the reaction is completed, wash it. Further specify that in (2), a highly insulating COC capacitive film with surface graft modification is obtained.

[0009] Further specify that in (1), the photoinitiator in the photoinitiator solution is one or a mixture of benzophenone, benzoin dimethyl ether, and isopropylbenzene thioxanthone, the solvent is acetone, and the mass ratio of the photoinitiator to the solvent is (0.01 - 0.05):(1 - 50).

[0010] Further specify that in (1), the surface irradiation pretreatment conditions are: the light source wavelength is 200 - 275 nm, the power is 10 - 30 W, and the time is 30 - 120 min.

[0011] Further specify that in (1), the protective atmosphere is nitrogen, helium, neon, or argon.

[0012] Further specify that in (1), ultrasonic cleaning is used for cleaning, and the power is 1000 - 2000 W.

[0013] Further specify that the raw material COC for preparing the COC film in (1) is copolymerized from norbornene and ethylene, and the content of norbornene is 30 - 80 mol%.

[0014] Further specify that the preparation method of the COC film is: under the conditions of a temperature of 25 - 120 °C and a rotation speed of 200 - 400 r / min, dissolve COC in an organic solvent to obtain a COC solution. After coating into a film, perform gradient temperature increase treatment to obtain the COC solution.

[0015] Even further specify that the organic solvent is one or a mixture of toluene, xylene, dimethylformamide, and propylene glycol methyl ether.

[0016] Even further specify that the gradient temperature increase treatment process is: at a heating rate of 1 - 5 °C / min, multi-step gradient increase the temperature to 25 - 120 °C, and the temperature interval for each segment is 20 - 35 °C, and keep each segment at a constant temperature for 120 - 720 min.

[0017] Further specify that in (2), the strong electron-deficient organic small molecule substances are one or a mixture of maleic anhydride, acrylic anhydride, and phthalic acid.

[0018] Further specify that in (2), the electron-donating organic small molecule substances are one or a mixture of vinyl acetate, styrene, butyl vinyl ether, and N-vinyl pyrrolidone.

[0019] It is further defined that the molar ratio of the strongly electron-deficient organic small molecule substance to the electron-donating organic small molecule substance in the reaction solution of (2) is (0.01-0.5):(0.01-0.55).

[0020] It is further defined that the irradiation grafting treatment conditions in (2) are: the wavelength of the light source is 200 to 275 nm, the power is 10 to 30 W, and the time is 5 to 60 min.

[0021] It is further defined that the protective atmosphere in (2) is nitrogen, helium, neon or argon.

[0022] It is further defined that the drying temperature in (2) is 30 to 60°C.

[0023] The second object of the present invention is to provide a high-insulation COC capacitor film prepared by the above method, which has a thickness of 6 to 20 μm.

[0024] The third object of the present invention is to provide an application of the above-mentioned high-insulation COC capacitor film, specifically for the preparation of an energy storage device under electrothermal coupling conditions.

[0025] Beneficial effects of the present invention:

[0026] The present invention first utilizes ultraviolet light to induce the initiator to capture hydrogen from the CH bond on the surface of the COC capacitor film to form carbon free radicals on the surface, thereby generating COC surface activation sites, and then, under the induction of far ultraviolet light, a grafting reaction occurs between strongly electron-deficient organic small molecules and electron-donating organic small molecules and the COC surface activation sites, and further utilizes the association between the strongly electron-deficient organic small molecules and the electron-donating organic small molecules to form a charge transfer complex on the surface of the COC film, thereby obtaining a high-insulation COC capacitor film with a surface grafted charge transfer complex. Compared with the prior art, the high-insulation COC capacitor film prepared by the present invention has the following advantages:

[0027] (1) The highly insulating COC capacitive film with surface-grafted charge transfer complex prepared by the present invention constructs a charge transfer complex by the association between a strong electron-withdrawing organic small molecule and an electron-donating organic small molecule, and is grafted onto the surface of the COC capacitive film under the action of far-ultraviolet light and a photoinitiator. By utilizing the electron delocalization effect and wide bandgap characteristics of the charge transfer complex, the height of the interfacial Schottky barrier is increased, and the electron injection effect under high temperature and high field is inhibited; meanwhile, the positive vertical ionization energy of the charge transfer complex can effectively capture the high-energy electrons injected at the electrode, avoiding the generation of secondary electrons caused by high-energy electrons hitting the COC macromolecular chain and resulting in electron avalanche, significantly reducing the conductance loss of the COC capacitive film and greatly improving the high-temperature energy storage performance, solving the problem of the sharp decline in energy storage performance caused by the aggravated carrier injection of traditional COC capacitive films under high temperature and high field, and improving the high-temperature cycling stability of the COC capacitive film. The test results show that at a temperature of 125 °C, when the charge-discharge efficiency is 89%, the energy storage density reaches 4.87 J / cm 3 , and at 200 kV / mm, after 50,000 cycle shocks, the energy storage efficiency still remains above 95%.

[0028] (2) The preparation process of the highly insulating COC capacitive film provided by the present invention is simple, with a mature large-scale preparation technology, and existing industrial equipment can meet the production requirements; moreover, it can maintain the flexibility and uniformity of the polymer material, effectively solving various challenges faced in industrialization such as agglomeration and deterioration of mechanical properties caused by doping modification, and mismatch of polymer matrix forming technology, providing a guiding idea for the large-scale preparation of all-organic dielectric films for high-temperature and high-field applications. Description of the Drawings

[0029] Figure 1 is the structural formula of the MAH / VAc charge transfer complex;

[0030] Figure 2 is the surface electrostatic potential cloud diagram and potential statistical distribution of the COC dielectric film prepared in Comparative Example 1 and the MAH / VAc charge transfer complex;

[0031] Figure 3 is the energy level structure diagram of the COC capacitive film prepared in Comparative Example 1 and the MAH / VAc charge transfer complex;

[0032] Figure 4 is the infrared spectrum comparison diagram of the highly insulating COC capacitive films prepared in Examples 1 to 4 and Comparative Example 1;

[0033] Figure 5 is the comparison diagram of the changing trends of the dielectric constant and dielectric loss of the highly insulating COC capacitive films prepared in Examples 1 to 4 and Comparative Example 1 with frequency;

[0034] Figure 6Comparison chart of leakage current density of high-insulation COC capacitor films prepared in Examples 1-4 and Comparative Example 1;

[0035] Figure 7 Comparison chart of leakage current density of high-insulation COC capacitor films prepared in Example 3 and Comparative Examples 1-2;

[0036] Figure 8 Schottky barrier fitting chart of high-insulation COC capacitor films prepared in Examples 1-4 and Comparative Example 1;

[0037] Figure 9 Comparison chart of breakdown field strength of high-insulation COC capacitor films prepared in Examples 1-4 and Comparative Example 1 at 125°C;

[0038] Figure 10 Comparison chart of breakdown field strength of high-insulation COC capacitor films prepared in Example 3 and Comparative Examples 1-3 at 125°C;

[0039] Figure 11 Comparison chart of high-temperature energy storage density and energy storage efficiency of high-insulation COC capacitor films prepared in Examples 1-4 and Comparative Example 1 at 125°C;

[0040] Figure 12 Comparison chart of high-temperature energy storage density and energy storage efficiency of high-insulation COC capacitor films prepared in Example 3 and Comparative Examples 1-3 at 125°C;

[0041] Figure 13 High-temperature cycle stability test chart of high-insulation COC capacitor film prepared in Example 3 at 125°C. Detailed implementation manners

[0042] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0043] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0044] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or selectively exclusive embodiment from other embodiments.

[0045] The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in this field and can be obtained by those skilled in the art through commercial channels without special instructions.

[0046] The COC used in the following examples and comparative examples was purchased from Polyplastics Trading Co., Ltd., Japan, and was copolymerized from norbornene and ethylene, with a norbornene content of 77 mol%.

[0047] Example 1

[0048] (1) Under the conditions of a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min, and the holding time for each stage of the holding process was 480 min, to prepare a COC film with a thickness of 12 μm.

[0049] (2) In a 20 ml conical flask, 0.12 g of benzophenone was dissolved in 4 g of acetone solvent, and the solution was stirred magnetically until it was clear to obtain a benzophenone solution.

[0050] (3) In a 20 ml beaker, 2.61 g of maleic anhydride and 2.15 g of vinyl acetate were mixed and dissolved in 4 g of acetone solvent, and a maleic anhydride / vinyl acetate charge transfer complex solution was prepared by magnetic stirring.

[0051] (4) The obtained COC film was placed in an ethanol solution and ultrasonically cleaned at a power of 1500 W. After the film surface was dried, it was placed in the benzophenone solution to adsorb benzophenone, and under a nitrogen atmosphere, it was irradiated under a far ultraviolet light source with a power of 3 kW and a wavelength of 254 nm for 30 min to obtain a surface-activated COC film.

[0052] (5) The surface-activated COC film was immersed in the maleic anhydride / vinyl acetate charge transfer complex solution, and under a nitrogen atmosphere, it was irradiated under an ultraviolet lamp with a power of 3 kW and a wavelength of 254 nm for 5 min to induce the graft copolymerization reaction of the charge transfer complex, and a maleic anhydride / vinyl acetate charge transfer complex was formed on the film surface. After the reaction was completed, it was cleaned with acetone solution. After the cleaning was completed, it was vacuum dried at 60 °C for 12 h to obtain a high-insulation COC capacitive film with maleic anhydride / vinyl acetate charge transfer complex grafted on the surface, denoted as COC-MAH / VAc-5.

[0053] Example 2

[0054] (1) Under the conditions of a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min. The holding time for each stage of the heat preservation process was 480 min, and a COC film with a thickness of 12 μm was prepared;

[0055] (2) In a 20 ml conical flask, 0.12 g of benzophenone was dissolved in 5 ml of acetone solvent and stirred magnetically until the solution was clear to obtain a benzophenone solution;

[0056] (3) In a 20 ml beaker, 2.61 g of maleic anhydride and 2.30 ml of vinyl acetate were mixed and dissolved in 5 ml of acetone solvent, and a 5 mol / L maleic anhydride / vinyl acetate charge transfer complex solution was prepared by magnetic stirring;

[0057] (4) The obtained COC film was placed in an ethanol solution and ultrasonically cleaned at a power of 1500 W. After the film surface was dried, it was placed in the benzophenone solution to adsorb benzophenone, and then irradiated under a far ultraviolet light source with a power of 3 kW and a wavelength of 254 nm in a nitrogen atmosphere for 30 min to obtain a surface-activated COC film;

[0058] (5) The surface-activated COC film was immersed in the maleic anhydride / vinyl acetate charge transfer complex solution and irradiated under an ultraviolet lamp with a power of 3 kW and a wavelength of 254 nm in a nitrogen atmosphere for 10 min to induce graft copolymerization of the charge transfer complex, and a maleic anhydride / vinyl acetate charge transfer complex was formed on the film surface. After the reaction, it was washed with acetone solution. After the washing was completed, it was vacuum dried at 60 °C for 12 h to obtain a highly insulating COC capacitive film with maleic anhydride / vinyl acetate charge transfer complex grafted on the surface, denoted as COC-MAH / VAc-10.

[0059] Example 3

[0060] (1) Under the conditions of a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min. The holding time for each stage of the heat preservation process was 480 min, and a COC film with a thickness of 12 μm was prepared;

[0061] In a 20 ml conical flask, 0.12 g of benzophenone was dissolved in 4 g of acetone solvent and stirred magnetically until the solution was clear to obtain a benzophenone solution;

[0062] (3) In a 20 ml beaker, 2.61 g of maleic anhydride and 2.15 g of vinyl acetate were mixed and dissolved in 4 g of acetone solvent. A maleic anhydride / vinyl acetate charge transfer complex solution was prepared by magnetic stirring.

[0063] (4) The obtained COC film was placed in an ethanol solution and ultrasonically cleaned at a power of 1500 W. After the film surface was dried, it was placed in a benzophenone solution to adsorb benzophenone. Under a nitrogen atmosphere, it was irradiated with a far-ultraviolet light source with a power of 3 kW and a wavelength of 254 nm for 30 min to obtain a surface-activated COC film.

[0064] (5) The surface-activated COC film was immersed in the maleic anhydride / vinyl acetate charge transfer complex solution and irradiated with an ultraviolet lamp with a power of 3 kW and a wavelength of 254 nm under a nitrogen atmosphere for 15 min to induce a graft copolymerization reaction of the charge transfer complex, forming a maleic anhydride / vinyl acetate charge transfer complex on the film surface. After the reaction, it was cleaned with an acetone solution. After cleaning, it was vacuum-dried at 60 °C for 12 h to obtain a high-insulation COC capacitive film with a surface-grafted maleic anhydride / vinyl acetate charge transfer complex, denoted as COC-MAH / VAc-15.

[0065] Example 4

[0066] (1) Under the conditions of a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min and a holding time of 480 min for each stage of the holding process, to prepare a COC film with a thickness of 12 μm.

[0067] (2) In a 20 ml conical flask, 0.12 g of benzophenone was dissolved in 4 g of acetone solvent and stirred magnetically until the solution was clear to obtain a benzophenone solution.

[0068] (3) In a 20 ml beaker, 2.61 g of maleic anhydride and 2.15 g of vinyl acetate were mixed and dissolved in 4 g of acetone solvent. A maleic anhydride / vinyl acetate charge transfer complex solution was prepared by magnetic stirring.

[0069] (4) The obtained COC film was placed in an ethanol solution and ultrasonically cleaned at a power of 1500 W. After the film surface was dried, it was placed in a benzophenone solution to adsorb benzophenone, and then irradiated under a far-ultraviolet light source with a power of 3 kW and a wavelength of 254 nm for 30 min in a nitrogen atmosphere to obtain a surface-activated COC film;

[0070] (5) The surface-activated COC film was immersed in a maleic anhydride / vinyl acetate charge transfer complex solution and irradiated under an ultraviolet lamp with a power of 3 kW and a wavelength of 254 nm for 20 min in a nitrogen atmosphere to induce graft copolymerization of the charge transfer complex and form a maleic anhydride / vinyl acetate charge transfer complex on the film surface. After the reaction, it was cleaned with an acetone solution. After cleaning, it was vacuum dried at 60 °C for 12 h to obtain a high-insulation COC capacitor film with a surface grafted maleic anhydride / vinyl acetate charge transfer complex, denoted as COC-MAH / VAc-20.

[0071] Comparative Example 1

[0072] The specific process for preparing the COC capacitor film in this comparative example is as follows:

[0073] At a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min and a holding time of 480 min for each holding process to prepare a COC film with a thickness of 12 μm, denoted as COC.

[0074] Comparative Example 2

[0075] The specific process for preparing the surface-grafted maleic anhydride COC capacitor film in this comparative example is as follows:

[0076] (1) At a temperature of 120 °C and 250 r / min, 2 g of COC was dissolved in 20 ml of xylene solvent to obtain a COC solution, which was then coated on a substrate and subjected to gradient temperature increase treatment. The gradient temperature increase was carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min and a holding time of 480 min for each holding process to prepare a COC film with a thickness of 12 μm;

[0077] (2) In a 20 ml conical flask, 0.12 g of benzophenone was dissolved in 4 g of acetone solvent and stirred magnetically until the solution was clear to obtain a benzophenone solution;

[0078] (3) In a 20-ml beaker, place 2.45 g of maleic anhydride in 4 g of acetone solvent, and prepare a maleic anhydride solution by magnetic stirring.

[0079] (4) Place the obtained COC film in an ethanol solution, perform ultrasonic cleaning at a power of 1500 W. After the film surface is dried, place it in a benzophenone solution to adsorb benzophenone. Under a nitrogen atmosphere, irradiate it under a far-ultraviolet light source with a power of 3 kW and a wavelength of 254 nm for 30 min to obtain a surface-activated COC film.

[0080] (5) Immerse the surface-activated COC film in the maleic anhydride solution, irradiate it under an ultraviolet lamp with a power of 3 kW and a wavelength of 254 nm under a nitrogen atmosphere for 15 min to induce the graft polymerization reaction of maleic anhydride. After the reaction is completed, wash it with acetone solution. After the washing is completed, dry it in vacuo at 60 °C for 12 h to obtain a surface-grafted maleic anhydride COC capacitive film, denoted as COC-MAH-15.

[0081] Comparative Example 3

[0082] The specific process for preparing a surface-grafted vinyl acetate COC capacitive film in this comparative example is as follows:

[0083] (1) Under the conditions of a temperature of 120 °C and 250 r / min, dissolve 2 g of COC in 20 ml of xylene solvent to obtain a COC solution, then coat it on a substrate, and perform gradient temperature increase treatment. The gradient temperature increase is carried out in four steps: 25 °C → 60 °C → 90 °C → 120 °C, with a heating rate of 5 °C / min and a holding time of 480 min for each stage of the holding process to prepare a COC film with a thickness of 12 μm.

[0084] (2) In a 20-ml conical flask, dissolve 0.12 g of benzophenone in 4 g of acetone solvent, and stir magnetically until the solution is clear to obtain a benzophenone solution.

[0085] (3) In a 20-ml beaker, place 2.15 g of vinyl acetate in 4 g of acetone solvent, and prepare a maleic anhydride solution by magnetic stirring.

[0086] (4) Place the obtained COC film in an ethanol solution, perform ultrasonic cleaning at a power of 1500 W. After the film surface is dried, place it in a benzophenone solution to adsorb benzophenone. Under a nitrogen atmosphere, irradiate it under a far-ultraviolet light source with a power of 3 kW and a wavelength of 254 nm for 30 min to obtain a surface-activated COC film.

[0087] (5) Immerse the surface-activated COC film in a vinyl acetate solution, irradiate it under a UV lamp with a power of 3 kW and a wavelength of 254 nm in a nitrogen atmosphere for 15 min to induce graft polymerization of vinyl acetate. After the reaction, wash it with acetone solution. After washing, dry it in vacuum at 60 °C for 12 h to obtain a surface-grafted maleic anhydride COC capacitive film, denoted as COC-VAc-15.

[0088] Effect Example

[0089] Perform structural characterization and performance testing on the highly insulating COC capacitive films obtained in Examples 1 to 4 and Comparative Examples 1 to 3. The specific test results and analysis are as follows:

[0090] (1) Figure 4 Figure for comparing the infrared spectra of the highly insulating COC capacitive films prepared in Examples 1 to 4 and Comparative Example 1. As can be seen from the figure, compared with the COC capacitive film prepared in Comparative Example 1, the highly insulating COC capacitive films with surface-grafted charge transfer complexes prepared in Examples 1 to 4 show new peaks at 1730 cm -1 and 1780 cm -1 corresponding to the stretching vibration of C=O in vinyl acetate molecules and the vibration absorption peak of C=O in maleic anhydride molecules respectively, indicating that the characteristic functional groups of maleic anhydride and vinyl acetate have been successfully introduced into the grafted film, proving that the charge transfer complex has been successfully grafted onto the COC capacitive film.

[0091] (2) Figure 5 Figure for comparing the changing trends of the dielectric constant and dielectric loss of the highly insulating COC capacitive films prepared in Examples 1 to 4 and Comparative Example 1 with frequency. As Figure 5 can be seen: Compared with the COC capacitive film prepared in Comparative Example 1, the polarization characteristics of the highly insulating COC capacitive film with surface-grafted charge transfer complexes are significantly changed due to the introduction of the charge transfer complex at 125 °C. The dielectric constant and dielectric loss show a trend of first increasing and then decreasing with the irradiation time. At 1 kHz, the dielectric constant of the highly insulating COC capacitive film with surface-grafted charge transfer complexes prepared in Example 3 reaches 2.57, and the tangent value of the dielectric loss angle is 8.34×10 -4 , still remaining at a relatively low level. Thus, it shows that surface-grafting the charge transfer complex can effectively improve the dielectric properties of the COC capacitive film.

[0092] (3) Figure 6 Figure for comparing the leakage current density of the highly insulating COC capacitive films prepared in Examples 1 to 4 and Comparative Example 1. As Figure 6It can be seen that: compared with the COC capacitive film prepared in Comparative Example 1, the high-insulation COC capacitive film with surface-grafted charge transfer complex has an overall reduction of one order of magnitude in leakage current density under the conditions of 125 °C and an electric field strength of 200 kV / mm. Among them, the leakage current density of the high-insulation COC capacitive film with surface-grafted charge transfer complex prepared in Example 3 reaches the lowest value of 5.41×10 -10 A / cm 2 , which is only 4.04% of the COC film (1.34×10 -8 A / cm 2 ) prepared in Comparative Example 1. This shows that surface grafting of charge transfer complex can reduce the high-temperature conductance loss of COC capacitive film.

[0093] (4) Figure 7 Figure 4 is a comparison chart of the leakage current density of the high-insulation COC capacitive films prepared in Example 3 and Comparative Examples 1-3. It can be seen from Figure 7 that: compared with the COC capacitive film prepared in Comparative Example 1, the COC capacitive film with surface-grafted maleic acid has a smaller reduction in conduction loss at high temperature. At 125 °C and 200 kV / mm, its leakage current density is reduced to 32.47% of the COC capacitive film; while the high-temperature leakage current density of the high-insulation COC capacitive film with surface-grafted charge transfer complex is 4.04% of the COC film. This shows that the COC capacitive film with surface-grafted charge transfer complex can effectively reduce the high-temperature conduction loss of COC.

[0094] (5) Figure 8 Figure 5 is a Schottky barrier fitting diagram of the high-insulation COC capacitive films prepared in Examples 1-4 and Comparative Example 1. It can be seen from Figure 8 that: the fitting quantity R 2 of the high-insulation COC capacitive film with surface-grafted charge transfer complex ranges between 0.980 and 0.994, indicating that the transport of carriers conforms to the Schottky emission mechanism. And, the intercept of the fitting straight line shows a trend of first decreasing and then increasing with the prolongation of irradiation time. The size of the intercept is inversely proportional to the size of the Schottky barrier. Among them, the intercept of the high-insulation COC capacitive film with surface-grafted charge transfer complex prepared in Example 3 is the smallest, -24.1, much lower than that of the COC capacitive film prepared in Comparative Example 1 (-21.2), indicating that it has the highest Schottky barrier height. This shows that after grafting charge transfer complex on the surface of the COC capacitive film, deep trap energy levels can be formed to limit the carrier migration rate and reduce the conductivity, while increasing the interface Schottky barrier to capture the charge injected by the metal electrode, thereby reducing the leakage current density.

[0095] (6) Figure 9 Figure 6 is a comparison chart of the breakdown field strength of the high-insulation COC capacitive films prepared in Examples 1-4 and Comparative Example 1 at 125 °C. It can be seen fromFigure 9 It can be seen that: compared with the COC capacitor film prepared in Comparative Example 1, the characteristic breakdown field strength of the highly insulating COC capacitor film with surface-grafted charge transfer complex is significantly improved. Among them, the characteristic breakdown field strength value of the highly insulating COC capacitor film with surface-grafted charge transfer complex prepared in Example 3 is as high as 644.1 kV / mm, which is 31.6% higher than that of the COC capacitor film. This shows that surface grafting of charge transfer complex can improve the high-temperature breakdown characteristics of the COC capacitor film.

[0096] (7) Figure 10 Figure for comparing the breakdown field strengths of the highly insulating COC capacitor films prepared in Example 3 and Comparative Examples 1 to 3 at 125 °C. Figure 10 It can be seen that: compared with the COC capacitor film prepared in Comparative Example 1, the breakdown field strength of the COC capacitor film with surface-grafted maleic anhydride at high temperature is improved less. At 125 °C, the characteristic breakdown field strength is 522.6 kV / mm, and compared with the COC capacitor film, its characteristic breakdown field strength is only increased by 9.3%; compared with the COC capacitor film prepared in Comparative Example 1, the breakdown field strength of the COC capacitor film with surface-grafted vinyl acetate at high temperature is improved less. At 125 °C, the characteristic breakdown field strength is 520.7 kV / mm, and compared with the COC capacitor film, its characteristic breakdown field strength is only increased by 9.0%; while the high-temperature characteristic breakdown field strength of the highly insulating COC capacitor film with surface-grafted charge transfer complex is increased by 31.6% compared with the COC film. This shows that the COC capacitor film with surface-grafted charge transfer complex can significantly improve the high-temperature breakdown characteristics of COC.

[0097] (8) Figure 11 Figure for comparing the high-temperature energy storage density and energy storage efficiency of the highly insulating COC capacitor films prepared in Examples 1 to 4 and Comparative Example 1 at 125 °C. Figure 11 It can be seen that: under the condition of 125 °C, compared with the COC capacitor film prepared in Comparative Example 1, the energy storage density and energy storage efficiency of the highly insulating COC capacitor film with surface-grafted charge transfer complex are significantly improved. Among them, the energy storage density of the highly insulating COC capacitor film with surface-grafted charge transfer complex prepared in Example 3 reaches the maximum value, which is 4.87 J / cm 3 , which is 2.76 times higher than that of the COC capacitor film, and the energy storage efficiency remains above 89%. This shows that surface grafting of charge complex significantly improves the high-temperature energy storage performance of the COC capacitor film.

[0098] (9) Figure 12 Figure for comparing the high-temperature energy storage density and energy storage efficiency of the highly insulating COC capacitor films prepared in Example 3 and Comparative Examples 1 to 3 at 125 °C. Figure 12It can be seen that: compared with the COC capacitive film prepared in Comparative Example 1, the energy storage density of the highly insulating COC capacitive film with surface-grafted charge transfer complex is increased by 192.8% compared with the COC capacitive film, and the energy storage efficiency is also better than that of the COC capacitive film. Although the energy storage density of the surface-grafted maleic anhydride COC capacitive film prepared in Comparative Example 2 is increased by 25.9% compared with the COC capacitive film, it is still inferior to the improvement effect of the surface-grafted charge transfer complex. Similarly, the energy storage density of the COC capacitive film with surface-grafted vinyl acetate prepared in Comparative Example 3 is increased by 28.7% compared with the COC capacitive film.

[0099] (10) Figure 13 Figure 125 is a high-temperature cycle stability test chart of the highly insulating COC capacitive film prepared in Example 3 at 125 °C. It can be seen from Figure 13 that: the highly insulating COC capacitive film with surface-grafted charge transfer complex can withstand 50,000 cycle impacts at 200 MV / m at 125 °C without insulation breakdown. This shows that the surface-grafted charge transfer complex enhances the structural stability of the COC capacitive film and has good high-temperature cycle stability.

[0100] (11)Regarding the performance differences of the highly insulating COC capacitive films prepared in Example 3, Comparative Example 2, and Comparative Example 3, further analysis of the MAH / VAc charge transfer complex was carried out. Assuming that a MAH / VAc charge transfer complex is formed between MAH and VAc as shown in the Figure 1 structural formula, the surface electrostatic potential cloud and potential of the COC capacitive film prepared in Comparative Example 1 and the MAH / VAc charge transfer complex were statistically distributed. The results are as shown in Figure 2 Figure, and it can be seen from Figure 2 Figure that: the overall potential distribution of the COC capacitive film prepared in Comparative Example 1 is relatively uniform, and the overall potential is neutral. Compared with the COC capacitive film, the overall potential of the MAH / VAc charge transfer complex has a large difference, indicating that a significant electron delocalization structure is formed inside the complex, and the oxygen atom in the MAH / VAc charge transfer complex shows a strong electron-attracting ability. This shows that grafting it onto the COC surface can attract the injected carriers at the electrode.

[0101] Figure 3 Figure 15 is the energy level structure diagram of the COC capacitive film prepared in Comparative Example 1 and the MAH / VAc charge transfer complex; it can be seen from Figure 3It can be seen that the vertical electron affinity of the COC capacitive film is negative, while that of the MAH / VAc charge transfer complex is positive. Therefore, it has a stronger electron capture ability, enabling the MAH / VAc complex to preferentially capture the high-energy electrons injected at the electrode, localize the electrons through the charge transfer mechanism, and thus avoid the generation of secondary electrons due to the impact of high-energy electrons on the COC macromolecular chain, resulting in electron avalanche. At the same time, the band gap of the MAH / VAc charge transfer complex is 6.75 eV, which is smaller than the vertical ionization energy of COC (7.62 eV) and the vertical ionization energy of the MAH / VAc charge transfer complex (7.72 eV). Therefore, when the MAH / VAc charge transfer complex undergoes an inelastic collision with high-energy electrons, the MAH / VAc charge transfer complex will absorb energy of 6.75 - 7.72 eV to enter the excited state, rather than ionize to generate secondary electrons. This shows that introducing a charge transfer complex on the COC surface can inhibit the generation and development of electron avalanche at the interface and improve the insulation performance of COC. This is also the fundamental reason why it is considered in this application that the formation of the MAH / VAc charge transfer complex between MAH and VAc plays a synergistic role in improving the energy storage performance of the COC capacitive film.

[0102] The above are only the preferred specific embodiments of the present invention. These specific embodiments are all different implementation manners based on the overall concept of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a high-insulation COC capacitor film, characterized in that Including: (1) Clean and dry the COC film, place it in a photoinitiator solution, and perform surface irradiation pretreatment under a far ultraviolet light source in a protective atmosphere to obtain a surface-activated COC film; (2) Immerse the surface-activated COC film in a reaction solution containing strong electron-deficient organic small molecule substances and electron-donating organic small molecule substances, and perform irradiation grafting treatment under a far ultraviolet light source in a protective atmosphere. After the reaction, wash and dry to obtain a highly insulating COC capacitor film with surface graft modification.

2. The preparation method according to claim 1, characterized in that, In the photoinitiator solution in (1), the photoinitiator is one or a mixture of benzophenone, benzoin dimethyl ether, and isopropylbenzene thioxanthone, the solvent is acetone, and the mass ratio of the photoinitiator to the solvent is (0.01 - 0.05):(1 - 50).

3. The preparation method according to claim 1, characterized in that, The surface irradiation pretreatment conditions in (1) are: the light source wavelength is 200 - 275 nm, the power is 10 - 30 W, and the time is 30 - 120 min.

4. The preparation method according to claim 1, wherein The raw material COC for preparing the COC film in (1) is copolymerized from norbornene and ethylene, and the norbornene content is 30 - 80 mol%.

5. The preparation method according to claim 1, characterized in that, In (2), the strong electron-deficient organic small molecule substance is one or a mixture of maleic anhydride, acrylic anhydride, and phthalic acid.

6. The preparation method according to claim 1, characterized in that, In (2), the electron-donating organic small molecule substance is one or a mixture of vinyl acetate, styrene, butyl vinyl ether, and N-vinylpyrrolidone.

7. The preparation method according to claim 1, wherein In the reaction solution of (2), the molar ratio of the strong electron-deficient organic small molecule substance to the electron-donating organic small molecule substance is (0.01 - 0.5):(0.01 - 0.55).

8. The preparation method according to claim 1, wherein, The irradiation grafting treatment conditions in (2) are: the light source wavelength is 200 - 275 nm, the power is 10 - 30 W, and the time is 5 - 60 min.

9. A high-insulation COC capacitive film prepared by the method according to any one of claims 1 to 8, characterized in that The thickness is 6 - 20 μm.

10. The application of the high-insulation COC capacitor film according to claim 9, characterized in that, For the preparation of an energy storage device under electrothermal coupling conditions.

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