Composite film material for energy storage capacitor, and preparation method and use thereof

Abstract

A film comprising a polydopamine (PDA) coated barium titanate (BT) filler dispersed in polyvinylidene fluoride (PVDF) where the PDA-BT forms a core-shell structure with BT as the core and PDA as the s

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of polymer composites, and in particular to a composite film material for an energy storage capacitor, and a preparation method and use thereof. BACKGROUND

[0002] Polymers are key energy storage materials for film capacitors. The technical indicators of electrical performance for the polymers have decisive effects on the energy storage and service performance of capacitors, especially the indicators such as dielectric constant, breakdown field strength, and energy storage density.

[0003] Polyvinylidene fluoride (PVDF) is theoretically very beneficial for increasing the energy storage density of a polymer material. However, the intrinsic ferroelectric polarization of PVDF and the high-dielectric constant ceramic filler bring great dielectric polarization, which leads to the sharp increase in a dielectric loss and the decrease in a breakdown field strength for PVDF / ceramic composites. This is because the insulation reduction caused by electron transport inside a material result in the rapid development of electrical branches and the premature breakdown of the material. SUMMARY

[0004] The present disclosure provides a composite film material for an energy storage capacitor, and a preparation method and use thereof. Single-layer film of the present disclosure has a prominent truncation effect for electrical branches.

[0005] The present disclosure provides a film, including PVDF and a barium titanate (BT)@polydopamine filler dispersed in the PVDF. The BT@polydopamine filler has a core-shell structure with BT as a core and polydopamine as a shell.

[0006] A polydopamine layer is amorphous, has a large number of functional groups such as amino and hydroxyl on its surface, and exhibits excellent compatibility with the PVDF (namely, strong bonding). Due to bonding effects such as hydrogen bonding between the polydopamine and the PVDF, it is easy to tightly combine the PVDF with the BT so as to improve the truncation effect for electrical branches.

[0007] In the composite film of the present disclosure, a prominent absorption effect of the polymethyl methacrylate (PMMA) film for electrical branches and the strong binding of the PVDF to the BT@polydopamine filler in the film play an excellent synergistic role in the truncation for electrical branches, and a release energy density produced accordingly is as high as 9.7 J / cm3 to 13.5 J / cm3, which is 191% to 304% higher than a discharge energy density of a pure PVDF substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 shows an X-ray diffraction (XRD) pattern of the BT@D nanoparticle obtained in Example 1;

[0009] FIG. 2 shows a transmission electron microscopy (TEM) image and an enlarged partial view of the BT@D nanoparticle obtained in Example 1;

[0010] FIG. 3 is a diagram illustrating the comparison of infrared spectra of the BT nanoparticle obtained in c of step (1) of Example 1 and the BT@D nanoparticle obtained in Example 1;

[0011] FIG. 4 is a diagram illustrating the comparison of XRD patterns of the BP composite films obtained in Comparative Examples 2 to 5;

[0012] FIG. 5 is a diagram illustrating the comparison of XRD patterns of the BDP composite films obtained in Examples 2 to 5;

[0013] FIG. 6 shows scanning electron microscopy (SEM) images of the BP composite films obtained in Comparative Examples 3 to 5 and the BDP composite films obtained in Examples 3 to 5;

[0014] FIG. 7 is a diagram illustrating the comparison of dielectric constants and dielectric losses of the BP composite films obtained in Comparative Examples 2 to 5;

[0015] FIG. 8 is a diagram illustrating the comparison of dielectric constants and dielectric losses of the BDP composite films obtained in Examples 2 to 5;

[0016] FIG. 9 shows SEM images of the composite films obtained in Example 6 and Comparative Example 6;

[0017] FIG. 10 is a diagram illustrating the comparison of dielectric constants and dielectric losses of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6;

[0018] FIG. 11 is a diagram illustrating the comparison of leakage current densities of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6;

[0019] FIG. 12 is a diagram illustrating the comparison of Weibull distributions of breakdown field strengths of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6;

[0020] FIG. 13 shows an electric branch simulation of the BP composite film obtained in Comparative Example 4;

[0021] FIG. 14 shows an electric branch simulation of the BDP composite film obtained in Example 4;

[0022] FIG. 15 shows an electric branch simulation of the composite film obtained in Example 6;

[0023] FIG. 16 is a diagram illustrating the comparison of a difference between a maximum electric displacement polarization value Dm and a residual polarization value Dr for each of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6; and

[0024] FIG. 17 is a diagram illustrating the comparison of release energy densities and charge / discharge efficiencies of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] The present disclosure provides a film, including PVDF and a BT@poly dopamine filler dispersed in the PVDF (wherein refers to “coated”, that is, BT@polydopamine refers to BT coated with polydopamine),

[0026] where the BT@polydopamine filler has a core-shell structure with BT as a core and poly dopamine as a shell.

[0027] In the present disclosure, a volume fraction of the BT@polydopamine filler in the film is 3% to 10%, and the volume fraction can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. A thickness of the poly dopamine in the BT@polydopamine filler is preferably 2 nm to 10 nm, and the thickness can be 2 nm, 4 nm, 6 nm, 8 nm, or 10 nm. A particle size of the BT is preferably 100 nm or less, and the particle size can be 20 nm, 40 nm, 60 nm, 80 nm, or 100 nm.

[0028] In the present disclosure, the BT@polydopamine filler is prepared by a process method preferably including:

[0029] subjecting BT, an aqueous solution of Tris-HCL, and dopamine hydrochloride to mixing, and then an oxidative polymerization and crosslinking reaction to obtain the BT@polydopamine filler.

[0030] In the present disclosure, the mixing preferably includes: subjecting BT and the aqueous solution of Tris-HCL to a first mixing to obtain a first mixture; and subjecting the first mixture and the dopamine hydrochloride to a second mixing to obtain a second mixture, and subjecting second mixture to the oxidative polymerization and crosslinking reaction.

[0031] In the present disclosure, a solid-to-liquid ratio of the BT to the aqueous solution of Tris-HCL is preferably in a range of 0.22 g: 200 mL to 0.27 g : 200 mL.

[0032] In the present disclosure, the BT is prepared by a process preferably including:

[0033] subjecting a BT raw material to wet ball-milling and drying in sequence.

[0034] In the present disclosure, the wet ball-milling is conducted for 4 h to 6 h, and the time for the wet ball-milling can be 4 h, 5 h, or 6 h. A solvent used for the wet ball-milling is preferably ethanol. The wet ball-milling is conducted at a rotational speed of preferably 600 r / min to 800 r / min, and the rotational speed could be 600 r / min, 650 r / min, 700 r / min, 750 r / min, or 800 r / min.

[0035] In the present disclosure, the drying is conducted at a temperature of preferably 60°C to 80°C, and the temperature can be 60°C, 65°C, 70°C, 75°C, or 80°C. The drying is conducted for preferably 10 h to 14 h, and the time can be 10 h, 11 h, 12 h, 13 h, or 14 h.

[0036] The solvent used for the wet ball-milling is removed during the drying.

[0037] In the present disclosure, the aqueous solution of Tris-HCL has a pH of 8.2 to 8.8, and the pH could be 8.2, 8.3, 8.4, 8.5, 8.6, 8.7, or 8.8. A concentration of Tris in the aqueous solution of Tris-HCL is preferably 9 mol / L to 11 mol / L, and the concentration could be 9 mol / L, 10 mol / L, or 11 mol / L.

[0038] In the present disclosure, the aqueous solution of Tris-HCL is prepared by a process preferably including:

[0039] Dissolving Tris in water to obtain a Tris solution.

[0040] Subjecting dilute hydrochloric acid and the Tris solution to a third mixing to obtain the aqueous solution of Tris-HCL.

[0041] In the present disclosure, the third mixing preferably includes: adding the dilute hydrochloric acid dropwise to the Tris solution.

[0042] In the present disclosure, a mass fraction of the dilute hydrochloric acid is preferably 16% to 20%, and the mass fraction could be 16%, 17%, 18%, 19%, or 20%.

[0043] In the present disclosure, the dropwise addition is preferably conducted under magnetic stirring. The magnetic stirring is conducted for preferably 5 min to 15 min, and the time could be 5 min, 8 min, 10 min, 12 min, or 15 min. The magnetic stirring is conducted at a rotational speed of preferably 80 r / min to 120 r / min, and the rotational speed could be 80 r / min, 90 r / min, 100 r / min, 110 r / min, or 120 r / min.

[0044] In the present disclosure, the first mixing preferably includes conducting cycles of ultrasonic mixing and a first magnetic stirring mixing, and a second magnetic stirring magnetic stirring-based mixing after the cycles are completed. In the present disclosure, there are preferably 3 to 5 cycles, and there could be 3, 4, or 5 cycles. In each cycle, the ultrasonic mixing is conducted at a power of preferably 150 W to 250 W independently, and the power could be independently 150 W, 180 W, 200 W, 220 W, or 250 W. In each cycle, the ultrasonic mixing is conducted for preferably 10 min to 20 min independently, and the time could be independently 10 min, 12 min, 15 min, 18 min, or 20 min. In each cycle, the first magnetic stirring mixing is conducted at a rotational speed of preferably 80 r / min to 160 r / min, and the rotational speed could be 80 r / min, 100 r / min, 120 r / min, 140 r / min, or 160 r / min. In each cycle, the first magnetic stirring mixing is conducted for a time of preferably 10 min to 20 min, and the time could be independently 10 min, 12 min, 15 min, 18 min, or 20 min.

[0045] In the present disclosure, the second magnetic stirring mixing is conducted at a rotational speed of preferably 80 r / min to 160 r / min, and the rotational speed could be 80 r / min, 100 r / min, 120 r / min, 140 r / min, or 160 r / min. The second magnetic stirring mixing is conducted for a time of preferably 10 h to 14 h, and the time could be 10 h, 11 h, 12 h, 13 h, or 14 h.

[0046] In the present disclosure, a mass ratio of the Tris to the dopamine hydrochloride is preferably in a range of 1: 0.125 to 1: 0.375, and the mass ratio could be 1: 0.125, 1: 0.15, 1: 0.2, 1: 0.25, 1: 0.3, or 1: 0.375.

[0047] In the present disclosure, the second mixing is preferably conducted under magnetic stirring. The magnetic stirring is conducted at a rotational speed of preferably 100 r / min to 300 r / min, and the rotational speed could be 100 r / min, 150 r / min, 200 r / min, 250 r / min, or 300 r / min. The magnetic stirring is conducted for a time of preferably 10 h to 20 h, and the time could be 10 h, 12 h, 14 h, 16 h, 18 h, or 20 h.

[0048] The oxidative polymerization and crosslinking reaction occur during the second mixing.

[0049] In the present disclosure, after the second mixing is completed, solid-liquid separation is preferably conducted to obtain a solid, and then the solid is washed, dried, and ground.

[0050] In the present disclosure, the washing preferably includes repeated washing with water, and the washing is conducted preferably 3 to 5 times.

[0051] In the present disclosure, the drying is conducted at a temperature of preferably 60 °C to 80 °C, and the temperature could be 60 °C, 70 °C, or 80 °C. The drying is conducted for a time of preferably 10 h to 14 h, and the time could be 10 h, 11 h, 12 h, 13 h, or 14 h.

[0052] In the present disclosure, the grinding is conducted for preferably 1 h to 2 h.

[0053] The present disclosure also provides a film prepared by the method as described in the above technical solutions, including:

[0054] mixing a solution of the PVDF and a dispersion of the BT@poly dopamine filler (which is called as fourth mixing) to obtain a mixture, coating the mixture, and drying.

[0055] In the present disclosure, the solution of the PVDF is prepared by a process preferably including:

[0056] subjecting the PVDF and a polar organic solvent to a fifth mixing, vacuuming, and standing under sealing.

[0057] In the present disclosure, the fifth mixing preferably includes: adding the PVDF to the polar organic solvent.

[0058] In the present disclosure, a solid-to-liquid ratio of the PVDF to the polar organic solvent is preferably 1 g : (4-7.5) mL, and the solid-to-liquid ratio could be 1 g : (4-7.5) mL, 1 g : (4-4.5) mL, 1 g : (4-5) mL, 1 g : (4-5.5) mL, 1 g : (4-6) mL, 1 g : (4-6.5) mL, 1 g : (4-7) mL, or 1 g : (4-7.5) mL. The polar organic solvent preferably includes N, N-dimethylformamide.

[0059] In the present disclosure, the adding is preferably conducted under magnetic stirring. The magnetic stirring is conducted at a rotational speed of preferably 300 r / min to 400 r / min, and the rotational speed of the magnetic stirring could be 300 r / min, 350 r / min, or 400 r / min. The magnetic stirring is conducted for preferably 2 h to 4 h, and the time could be 2 h, 3 h, or 4 h.

[0060] In the present disclosure, the vacuuming is conducted for preferably 0.5 h to 1.5 h, and the time of the vacuuming could be 0.5 h, 1 h, or 1.5 h.

[0061] In the present disclosure, the standing under sealing is conducted for preferably 1 h to 3 h, and the time of the standing under sealingcould be 1 h, 2 h, or 3 h.

[0062] In the present disclosure, the dispersion of the BT@polydopamine filler is prepared by a process preferably including:

[0063] dispersing the BT@polydopamine filler in a polar organic solvent.

[0064] In the present disclosure, a solid-to-liquid ratio of the BT@polydopamine filler to the polar organic solvent is preferably 1 g: (7-35.5) mL, and the solid-to-liquid ratio could be 0.31 g: (9-11) mL, 0.53 g: (9-11) mL, 0.76 g: (9-11) mL, or 1.13 g: (9-11) mL. The polar organic solvent preferably includes N, N-dimethylformamide.

[0065] In the present disclosure, the dispersing is preferably conducted under ultrasound and magnetic stirring that are conducted circularly. In the present disclosure, there are preferably 3 to 5 cycles, and there could be 3, 4, or 5 cycles. In each cycle, the ultrasound is conducted at a power preferably of 150 W to 250 W independently, and the power of the ultrasound could be 150 W, 180 W, 200 W, 220W, or 250 W. In each cycle, the ultrasound is conducted for preferably 10 min to 20 min independently, and the time of the ultrasound could be 10 min, 12 min, 15 min, 18 min, or 20 min. In the present disclosure, in each cycle, the magnetic stirring is conducted at a rotational speed of preferably 80 r / min to 160 r / min independently, and the rotational speed of the magnetic stirring could be 80 r / min, 100 r / min, 120 r / min, 140 r / min, or 160 r / min. In each cycle, the magnetic stirring is conducted for preferably 10 min to 20 min independently, and the time of the magnetic stirring could be 10 min, 12 min, 15 min, 18 min, or 20 min.

[0066] In the present disclosure, the fourth mixing preferably includes: adding the solution of the PVDF to the dispersion of the BT@polydopamine filler, subjecting a resulting mixture to vacuuming, and standing under sealing.

[0067] In the present disclosure, a volume fraction ratio of the PVDF in the solution of the PVDF to the BT@polydopamine filler in the dispersion of the BT@polydopamine filler is preferably 9: Ito 32.3: 1, and the volume fraction ratio is preferably 9:1, 13.3:1, 19:1, or 32.3:1.

[0068] In the present disclosure, the adding is conducted at a rate of preferably 0.2 mL / min to 0.5 mL / min, and the rate of the adding could be 0.2 mL / min, 0.3 mL / min, 0.4 mL / min, or 0.5 mL / min. The adding is conducted preferably under magnetic stirring. The magnetic stirring is conducted at a rotational speed of preferably 400 r / min to 600 r / min, and the rotational speed of the magnetic stirring could be 400 r / min, 450 r / min, 500 r / min, 550 r / min, or 600 r / min. The magnetic stirring is conducted for preferably 4 h to 8 h, and the time of the magnetic stirring could be 4 h, 5 h, 6 h, 7 h, or 8 h.

[0069] In the present disclosure, the vacuuming is conducted for preferably 0.5 h to 1.5 h, and the time of the vacuuming could be 0.5 h, 1 h, or 1.5 h.

[0070] In the present disclosure, the standing under sealing is conducted for preferably 10 h to 14 h, and the time of the standing under sealing could be 10 h, 11 h, 12 h, 13 h, or 14 h.

[0071] In the present disclosure, the drying is conducted at a temperature of preferably 50 °C to 70 °C, and the temperature could be 50°C, 60°C, or 70°C. The drying is conducted for preferably 3 min to 8 min, and the time could be 3 min, 4 min, 5 min, 6 min, 7 min, or 8 min.

[0072] In the present disclosure, a dry film produced after the drying is preferably cooled to room temperature to obtain a cooled film.

[0073] In the present disclosure, the cooled film is preferably subjected to oven-drying. The oven-drying is conducted at a temperature of preferably 60 °C to 80 °C, and the temperature could be 60 °C, 70 °C, or 80 °C. The oven-drying is conducted for preferably 20 h to 26 h, and the time could be 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, or 26 h.

[0074] The present disclosure also provides a composite film, including a first PMMA film, a film, and a second PMMA film that are stacked sequentially, where the film is the film as described in the above technical solutions or a film prepared by the method as described in the above technical solutions.

[0075] In the present disclosure, thicknesses of the first PMMA film, the film, and the second PMMA film each are preferably 9 pm to 11 pm independently, and the thicknesses of the first PMMA film, the film, and the second PMMA film could be independently 9 pm, 10 pm, or 11 pm.

[0076] In the present disclosure, the composite film is prepared by a process preferably includeing:

[0077] subjecting a first PMMA solution to first coating and first drying to form the first PMMA film;

[0078] mixing a solution of PVDF and a dispersion of a BT@polydopamine filler (which is called as fourth mixing), then coating a resulting mixture on the first PMMA film, and drying to form the film; and

[0079] subjecting a second PMMA solution to second coating and second drying on the film to form the second PMMA film, obtaining the composite film.

[0080] In the present disclosure, the first PMMA solution is prepared by a process preferably including the following step:

[0081] subjecting PMMA and a polar organic solvent to sixth mixing and then standing under sealing.

[0082] In the present disclosure, a solid-to-liquid ratio of the PMMA to the polar organic solvent is preferably 1 g: (4-18) mL, and the solid-to-liquid ratio could be 1 g: 4 mL to 1 g: 18 mL, 1 g: 6 mL, 1 g: 8 mL, 1 g: 10 mL, 1 g: 12 mL, 1 g: 14 mL, 1 g: 16 mL, or 1 g: 18 mL.

[0083] In the present disclosure, the sixth mixing is preferably conducted under magnetic stirring. The magnetic stirring is conducted at a rotational speed of preferably 300 r / min to 400 r / min, and the rotational speed of the magnetic stirring could be 300 r / min, 350 r / min, or 400 r / min. The magnetic stirring is conducted for preferably 4 h to 8 h, and the time of the magnetic stirring could be 4 h, 5 h, 6 h, 7 h, or 8 h.

[0084] In the present disclosure, the standing under sealing is conducted for preferably 1 h to 3 h, and the time of the sealed standing could be 1 h, 2 h, or 3 h.

[0085] In the present disclosure, the first drying is conducted at a temperature of preferably 50 °C to 70 °C, and the temperature of the first drying could be 50 °C, 60 °C, or 70 °C. The first drying is conducted for preferably 3 min to 8 min, and the time of the first drying could be 3 min, 4 min, 5 min, 6 min, 7 min, or 8 min.

[0086] In the present disclosure, a dry film produced after the first drying is preferably cooled to room temperature to form the first PMMA film.

[0087] The raw materials for the film are coated on the first PMMA film and dried to form the film.

[0088] A method for preparing the film has been discussed early and will not be repeated here.

[0089] In the present disclosure, after the film is formed, a second PMMA solution is subjected to second coating and second drying on the film to form the second PMMA film, so as to obtain the composite film.

[0090] Preferably, the second PMMA solution, the second coating, and the second drying are independently consistent with the first PMMA solution, the first coating, and the first drying, respectively.

[0091] In the present disclosure, after the second drying, the method further includes preferably conducting third drying to obtain the composite film.

[0092] In the present disclosure, the third drying is conducted at a temperature of preferably 60 °C to 80 °C, and the temperature of the third drying could be 60 °C, 70 °C, or 80 °C. The third drying is conducted for preferably 20 h to 26 h, and the time of the third drying could be 20 h, 21 h, 22 h, 23 h, 24 h, 25 h, or 26 h.

[0093] The composite film material for an energy storage capacitor and the preparation method and use thereof provided by the present disclosure will be described in detail with reference to the following examples. However, these examples should not be construed as limiting the scope of the present disclosure.

[0094] PMMA(CAS NO 9011-14-7, No. P141444) - Shanghai Aladdin Biochemical technology Co., Ltd, China.

[0095] PVDF (model: FR904) - Shanghai Sanaifu New Material Technology Co., Ltd, China.

[0096] Example 1

[0097] (1) Preparation of BT@D

[0098] a. 0.24 g of Tris was mixed with 200 mL of deionized water to form a solution A.

[0099] b. Dilute hydrochloric acid with a mass fraction of 18% was added dropwise to the solution A. A resulting mixture was subjected to magnetic stirring at a stirring speed of 100 r / min for 10 min. A pH was adjusted to 8.5 to form a Tris-HCL aqueous solution B with a Tris concentration of 10 mmol / L.

[0100] c. BT nanoparticles were ball-milled at a rotational speed of 700 r / min for 5 h with ethanol as a solvent. A liquid produced after the ball-milling was oven-dried at 70 °C for 12 h to produce BT nanoparticles C with a particle size of 80 nm.

[0101] d. 1.5 g of the BT nanoparticles C was added to the Tris-HCL aqueous solution B, and 4 cycles of ultrasound and magnetic stirring were conducted. In each cycle, the ultrasound was conducted at a power of 200 W for 15 min, and the magnetic stirring was conducted at a stirring speed of 120 r / min for 15 min. After the 4 cycles were completed, magnetic stirring was further conducted for 12 h to obtain a solution D.

[0102] e. 0.1 g of dopamine hydrochloride was added to the solution D, and a resulting mixture was subjected to magnetic stirring at a stirring speed of 200 r / min for 12 h to obtain a reaction solution E.

[0103] f. A supernatant produced in the reaction solution E was poured off, and a precipitate was washed with deionized water 4 times to obtain a washed powder.

[0104] g. The washed powder was oven-dried at 80 °C for 12 h and then ground for 1 h to obtain a BT@polydopamine nanoparticle filler F with a core-shell structure (which was called as BT@D). A polydopamine coating layer of the BT@polydopamine nanoparticle filler F has a thickness of 2 nm.

[0105] An XRD analysis was conducted for the BT@D obtained in Example 1, and results are shown in FIG. 1.

[0106] It can be seen from FIG. 1 that, in a 2-theta diffraction angle range of 10° to 90°, the typical diffraction peaks of crystal planes (100), (110), (111), (200), (210), (211), (220), (300), (310), (311), and (222) appear, indicating that the BT@D particle is completely crystalline and free of impurities, and is a typical perovskite BT crystal.

[0107] A TEM analysis and local enlargement were conducted for the BT@D obtained in Example 1, and results are shown in FIG. 2.

[0108] It can be seen from FIG. 2 that the core of the BT@D particle is a spheroid BT particle with a diameter of about 80 nm, and an amorphous shell D is coated on the BT core particle to produce the BT@D particle with a core-shell structure and a shell thickness of about 2 nm.

[0109] An infrared spectroscopy analysis was conducted for the BT nanoparticle obtained in c of the step (1) and the B T@D nanoparticles in Example 1, and results are shown in FIG. 3.

[0110] It can be seen from FIG. 3 that, after the BT nanoparticle was treated with dopamine, a strong benzene ring vibration absorption peak appears at 1,444 cm'1 and a typical CH vibration absorption peak appears at 2,976 cm'1, indicating that a shell of the BT@D particle is polydopamine. In addition, a hydroxyl OH bond vibration absorption peak appears at 3,431 cm'1, indicating that surfaces of the BT and BT@D nanoparticles obtained in Example 1 have hydroxyl groups with a large surface activity.

[0111] Example!

[0112] (1) This step was the same as step (1) in Example 1.

[0113] (2) Preparation of solutions

[0114] a. Under magnetic stirring, 2 g of a PVDF powder was added slowly to an Erlenmeyer flask with 14 mL of N,N-dimethylformamide solvent. A resulting mixture was subjected to magnetic stirring at a stirring speed of 350 r / min for 3 h, then vacuuming for 1 h, and standing under sealing for 2 h to obtain a PVDF solution H.

[0115] b. 0.31 g of BT@D was added to an Erlenmeyer flask with 10 mL of N,N-dimethylformamide solvent. 4 cycles of ultrasound and magnetic stirring were conducted to obtain a mixed solution I. In each cycle, the ultrasound was conducted at a power of 200 W for 15 min, and the magnetic stirring was conducted at a stirring speed of 100 r / min for 15 min.

[0116] c. 14 mL of the PVDF solution H was slowly added at a rate of 0.3 mL / min to 10 mL of the mixed solution I (a volume fraction ratio of the PVDF in the PVDF solution H to the BT@D filler F in the mixed solution I was 32.3:1). The mixed solution I was kept under magnetic stirring. The magnetic stirring was conducted at a stirring speed of 500 r / min for 6 h. Then a resulting solution was subjected to vacuuming for 1 h and standing under sealing for 12 h to obtain a PVDF filler interlayer mixed solution J.

[0117] (3) Single-layer composite film

[0118] The PVDF filler interlayer mixed solution J obtained in the step (2) was coated (with a coating thickness of 11 pm) on a clean glass plate, then oven-dried at 60 °C for 5 min, and cooled to room temperature, and then oven-dried at 80 °C for 24 h to obtain the single-layer composite film denoted as 3 vol.% BDP

[0119] Examples

[0120] This example was substantially the same as those in Example 2: except that in b of step (2), the amount of BT@D was 0.53 g, that is, a volume fraction ratio of the PVDF in the PVDF solution H to the BT@D filler F in the mixed solution I was 19:1.

[0121] A single-layer composite film produced in this example was denoted as 5 vol.% BDP.

[0122] Example 4

[0123] This example was substantially the same as those in Example 2: except that in b of step (2), the amount of BT@D was 0.76 g, that is, a volume fraction ratio of the PVDF in the PVDF solution H to the BT@D filler F in the mixed solution I was 13.3:1.

[0124] A single-layer composite film produced in this example was denoted as 7 vol.% BDP.

[0125] Example 5

[0126] This example was substantially the same as those in Example 2: except that in b of step (2), the amount of BT@D was 1.13 g, that is, a volume fraction ratio of the PVDF in the PVDF solution H to the BT@D filler F in the mixed solution I was 9:1.

[0127] A single-layer composite film produced in this example was denoted as 10 vol.% BDP.

[0128] Example 6

[0129] (1) This step was the same as step (1) in Example 1.

[0130] (2) Preparation of solutions

[0131] 3 g of PMMA was added to 18 mL of the N,N-dimethylformamide solvent, and a resulting mixture was subjected to magnetic stirring at a stirring speed of 350 r / min for 6 h to obtain a completely dissolved solution. Then the completely dissolved solution was subjected to standing under sealing for 2 h to obtain a PMMA outer layer solution G.

[0132] The solutions H, I, and J were the same as the corresponding solutions in Example 2.

[0133] (3) Three-layer composite film

[0134] a. The PMMA outer layer solution G was coated (with a coating thickness of 11 pm) on a clean glass plate, then oven-dried at 60 °C for 5 min, and cooled to room temperature. Then, the PVDF filler interlayer mixed solution J obtained in Example 4 was coated (with a coating thickness of 11 pm), then oven-dried at 60 °C for 5 min, and cooled to room temperature. Then the PMMA outer layer solution G was coated (with a coating thickness of 11 pm) and then oven-dried at 6 0°C for 5 min.

[0135] b. A three-layer film formed in the above step and the glass plate together were oven-dried at 80 °C for 24 h to obtain the three-layer composite film (PMMA-BDP-PMMA) with a thickness of 30 pm.

[0136] Comparative Example 1

[0137] Under magnetic stirring, 2 g of a PVDF powder was added slowly to 14 mL of the N,N-dimethylformamide solvent. A resulting mixture was subjected to magnetic stirring at a stirring speed of 350 r / min for 3 h, then vacuuming for 1 h, and standing under sealing for 2 h to obtain a PVDF solution H.

[0138] The PVDF solution H obtained in the above step was coated (with a coating thickness of it 11 um) on a clean glass plate and then oven-dried at 80 °C for 24 h to obtain a pure PVDF composite film denoted as PVDF.

[0139] Comparative Example 2

[0140] BT nanoparticles were subjected to wet ball-milling for 5 h at a rotational speed of 700 r / min with ethanol as a solvent. A liquid produced after the wet ball-milling was oven-dried at 70 °C for 12 h to produce BT nanoparticles C with a particle size of 80 nm.

[0141] This comparative example was substantially the same as those in Example 2: except that the BT@D filler F in Example 2 was replaced with a BT particle C.

[0142] A BT nanoparti cl e / PVDF single-layer composite film produced in this comparative example was denoted as 3 vol.% BP.

[0143] Comparative Example 3

[0144] This comparative example was substantially the same as those in Example 3: except that the BT@D filler F in Example 3 was replaced with a BT particle C.

[0145] A single-layer composite film produced in this comparative example was denoted as a 5 vol.% BP composite film.

[0146] Comparative Example 4

[0147] This comparative example was substantially the same as those in Example 4: except that the BT@D filler F in Example 4 was replaced with a BT particle C.

[0148] A single-layer composite film produced in this comparative example was denoted as a 7 vol.% BP composite film.

[0149] Comparative Example 5

[0150] This comparative example was substantially the same as those in Example 5: except that the BT@D filler F in Example 5 was replaced with a BT particle C.

[0151] A single-layer composite film produced in this comparative example was denoted as a 10 vol.% BP composite film.

[0152] An XRD analysis was conducted for the BT nanoparticle / PVDF single-layer composite films obtained in Comparative Examples 2 to 5, and results are shown in FIG. 4.

[0153] It can be seen from FIG. 4 that these composite films all have obvious PVDF and BaTiOs phase diffraction peaks, indicating that these composite films are produced through the compounding of the two phases. With the increasing of the BaTiCh concentration, a BaTiCh phase diffraction peak for the BP composite films in Comparative Examples 2 to 5 is enhanced, while a PVDF phase diffraction peak decreases first and then increases. That is, the PVDF phase diffraction peak of the BP composite film obtained in Comparative Example 4 has a minimum intensity when a filling amount is 7 vol.%.

[0154] An XRD analysis was conducted for the BDP composite films obtained in Examples 2 to 5, and results are shown in FIG. 5.

[0155] It can be seen from FIG. 5 that the BDP composite films all are produced mainly by compounding a BaTiCh phase and a PVDF phase, indicating that the BaTiO3@D remains a prominent crystal structure in the PVDF substrate. With the increasing of the filler concentration, an intensity of a BaTiOs phase diffraction peak for the BDP composite films obtained in Examples 2 to 5 increases. Compared with the XRD patterns of the BP composite films obtained in Comparative Examples 2 to 5, the XRD patterns of the BDP composite films do not have the diffraction peak of polydopamine, indicating that a D shell coated on a BT particle is amorphous.

[0156] A SEM analysis was conducted for the BP composite films obtained in Comparative Examples 3 to 5 and the BDP composite films obtained in Examples 3 to 5, and results are shown in FIG. 6. (a) in FIG. 6 shows SEM images of the BP composite films in Comparative Examples 3 to 5, and (b) in FIG. 6 shows SEM images of the BDP composite films in Examples 3 to 5.

[0157] It can be seen from (a) in FIG. 6 that, when the concentration of BT increases to 7 vol.%, the filler in the BP composite film obtained in Comparative Example 4 undergoes agglomeration, and the agglomeration is obvious in Comparative Example 5.

[0158] It can be seen from the SEM images of the BDP composite films in Examples 3 to 5 shown in (b) of FIG. 6 that, only when a concentration of the BT@D filler increases to 10 vol.%, the filler in the BDP composite film obtained in Example 5 undergoes mild agglomeration. This is because a large surface activity of a polydopamine outer layer increases the compatibility of the filler with the PVDF substrate material.

[0159] Dielectric constants and dielectric losses of the BP composite films obtained in Comparative Examples 2 to 5 were measured, and results are shown in FIG. 7.

[0160] It can be seen from FIG. 7 that the dielectric constants and dielectric losses of the BP composite films are dependent on a frequency and a filling amount to some extent. With the increasing of the frequency, the dielectric constants for the BP composite films decrease stepwise, and the dielectric loss decreases first and then increases. With the increasing of a filling amount, the dielectric constants and the dielectric losses for the BP composite films obtained in Comparative Examples 2 to 5 both increases. In the whole test frequency range, the BP composite film obtained in Comparative Example 4 has a dielectric constant of 13.8 to 18.9 and a dielectric loss of 0.03 to 0.23, indicating the superior characteristics of a high dielectric constant and a low dielectric loss.

[0161] Dielectric constants and dielectric losses of the BDP composite films obtained in Examples 2 to 5 were measured, and results are shown in FIG. 8.

[0162] It can be seen from FIG. 8 that the dielectric constants and dielectric losses of the BDP composite films are dependent on a frequency and a filling amount to some extent. With the increasing of the frequency, the dielectric constants for the BDP composite films decrease stepwise, and the dielectric losses decrease first and then increase. With the increasing of a filling amount, the dielectric constants increase and the low-frequency dielectric losses first decrease and then increase for the BDP composite films obtained in Examples 2 to 5. In the whole test frequency range, the BDP composite film obtained in Example 4 has a dielectric constant of 14 to 19.5 and a dielectric loss of 0.027 to 0.17. Compared with the material obtained in Comparative Example 4, the dielectric constant of the BDP composite film increases and the dielectric loss of the BDP composite film decreases, indicating that the BT@D filler with a “core-shell” structure can significantly improve the dielectric properties of a PVDF composite film.

[0163] Comparative Example 6

[0164] (1) This step was the same as step (1) in Example 1.

[0165] (2) Preparation of solutions

[0166] a. Under magnetic stirring, 2 g of a PVDF powder was added slowly at a rate of 80 mg / min to an Erlenmeyer flask with 14 mL of the N,N-dimethylformamide solvent. A resulting mixture was subjected to magnetic stirring at a stirring speed of 350 r / min for 3 h, then vacuuming for 1 h, and standing under sealing for 2 h to obtain a PVDF solution H.

[0167] (3) Three-layer nanocomposite film

[0168] This comparative example was substantially the same as those in Example 6: except that the PMMA outer layer solution G was replaced with the PVDF solution H.

[0169] A three-layer composite film produced in this comparative example was PVDF-7 vol.% BT@D / PVDF-PVDF, which is denoted as PVDF-BDP-PVDF and has a thickness of 30 pm.

[0170] A SEM analysis was conducted for the composite films obtained in Example 6 and Comparative Example 6, and results are shown in FIG. 9.

[0171] It can be seen from FIG. 9 that the filler BDP is randomly dispersed in the PVDF substrate as an intermediate layer and is well bonded with the PVDF substrate material. And there is a distinct layered interface in the two three-layer composite films.

[0172] Dielectric constants of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6 were measured, and results are shown in FIG. 10.

[0173] It can be seen from FIG. 10 that a dielectric constant of the composite film obtained in Example 6 is 5.6 to 7.5, which is reduced by 6.3% to 6.7% compared with 6 to 8 of the PVDF film obtained in Comparative Example 1. A dielectric constant of the composite film obtained in Comparative Example 6 is 7 to 9, which is 12.5% to 16.7% higher than the dielectric constant of the PVDF film. The BDP single-layer composite film obtained in Example 4 has a maximum dielectric constant of 14 to 19.3.

[0174] In addition, the composite film obtained in Example 6 has a minimum dielectric loss of 0.03 to 0.06, which is 50% to 65% lower than a dielectric loss of the pure PVDF material. It can be seen that the three-layer composite film structure could significantly reduce a dielectric loss on the basis of stabilizing a dielectric constant.

[0175] Leakage current densities of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6 were tested, and results are shown in FIG. 11.

[0176] It can be seen from FIG. 11 that the composite film obtained in Comparative Example 6 has a maximum leakage current of 1.4 x 10'6 A / cm2to 9.2 x 10'6 A / cm2, which is higher than a leakage current of 0.74 x 10'6 A / cm2 to 6.73 x 10'6 A / cm2 for the PVDF film obtained in Comparative Example 1. A leakage current of the BDP single-layer composite film obtained in Example 4 is lower than the leakage current of the PVDF film, and is 0.61 x 10’6 A / cm2 to 4.61 x 10’6 A / cm2. In contrast, the composite film obtained in Example 6 has a minimum leakage current of 0.32 x 10'6 A / cm2 to 2.94 x 10'6 A / cm2, which is 56.3% to 56.8% lower than the leakage current of the PVDF material.

[0177] Weibull distributions of breakdown field strengths of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6 are shown in FIG. 12.

[0178] It can be seen from FIG. 12 that, compared with the pure PVDF film, Eb of the BDP film decreases from 283 MV / m to 272 MV / m. Compared with the pure PVDF film, Eb values of the PMMA-BDP-PMMA composite film and the PVDF-BDP-PVDF three-layer composite film increase by 16.6% and 7.8%, respectively, indicating that the PMMA-BDP-PMMA three-layer film structure obtained in Example 6 could significantly improve the breakdown characteristics of the film.

[0179] An electric branch simulation of the BP composite film obtained in Comparative Example 4 is shown in FIG. 13. (a) in FIG. 13 is an electric branch simulation of the BP composite film at 16 s, and (b) in FIG. 13 is an enlarged partial view of (a) in FIG. 13.

[0180] It can be seen from FIG. 13 that an electrical branch of the BP single-layer composite film has developed rapidly, the filler and the PVDF substrate have been broken down at 16 s, and an electrically-conductive path of the electric branch is wide. In particular, the development of the electrical branch could extend into the BT nanoparticle, which increases the breakdown speed for the BP composite film.

[0181] An electrical branch simulation of the BDP composite film obtained in Example 4 is shown in FIG. 14. (a) in FIG. 14 is an electrical branch simulation of the BDP composite film at 16 s, and (b) in FIG. 14 is an enlarged partial view of (a) in FIG. 14.

[0182] It can be seen from FIG. 14 that the BDP composite film has a narrower electrical branch breakdown path than the BP single-layer composite film obtained in Comparative Example 4. Moreover, a development path of electrical branches is blocked by the polydopamine D coating layer, indicating that the polydopamine D layer coated on the BT filler has obvious blocking and buffering effects on the development of electrical branches.

[0183] An electrical branch simulation of the composite film obtained in Example 6 is shown in FIG. 15. (a) in FIG. 15 is an electrical branch simulation of the BDP composite film at 16 s, and (b) in FIG. 15 is an enlarged partial view of (a) in FIG. 15.

[0184] It can be seen from FIG. 15 that a speed of electrical branches entering into the intermediate layer from the outer layer is reduced, which is mainly manifested in the thinning of electrical branches. This is because the linear PMMA polymer outer layer exhibits a weakening effect for charge transport and an absorption effect for electrical branches to reduce the breakdown energy. In addition, it can be seen from the enlarged partial view that the remaining electrical branches after the absorption are truncated by the polydopamine shell, indicating a synergistic effect of the PMMA-BDP-PMMA three-layer composite film.

[0185] FIG. 16 is a comparison diagram of a difference between a maximum electric displacement polarization value Dm and a residual polarization value Dr for each of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6.

[0186] It can be seen from FIG. 16 that, under the same electric field, differences between maximum electric displacement polarization values Dm and residual polarization values Dr of the composite films rank as follows: PMMA-BDP-PMMA >PVDF-BDP-PVDF >BDP >PVDF. The larger the difference, the greater the energy storage density and the better the energy storage performance. Therefore, it can be known that the PMMA-BDP-PMMA three-layer composite film obtained in Example 6 exhibits the optimal energy storage performance, and has a polarization difference Dm-Dr of 6.8 pC / cm2.

[0187] FIG. 17 is a comparison diagram of release energy densities and charge / discharge efficiencies of the PVDF film obtained in Comparative Example 1 and the composite films obtained in Examples 4 and 6 and Comparative Example 6.

[0188] It can be seen from FIG. 17 that, at 325 kV / mm, the PMMA-BDP-PMMA three-layer composite film has a maximum release energy density of 10.4 J / cm3 that is 206% higher than the release energy density of the pure PVDF, and an energy storage efficiency of 78.3% that is 236% higher than the energy storage efficiency of the pure PVDF. It can be seen that the linear PMMA polymer obtained in Example 6 can comprehensively optimize the energy storage density and efficiency of the material when used as outer layers of the PMMA-BDP-PMMA three-layer composite structure.

[0189] The above are merely preferred embodiments of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the scope of the present disclosure.

Claims

1. A film, comprising polyvinylidene fluoride (PVDF) and a barium titanate (BT)@polydopamine filler dispersed in the PVDF,wherein the BT@polydopamine filler has a core-shell structure with BT as a core and poly dopamine as a shell.

2. The film according to claim 1, wherein a volume fraction of the BT@polydopamine filler in the film is in a range of 3% to 10%.

3. The film according to claim 1 or 2, wherein in the BT@poly dopamine filler, the poly dopamine has a thickness of 2 nm to 10 nm, and the BT has a particle size of not larger than 100 nm.

4. A method for preparing the film according to any one of claims 1 to 3, comprising the following steps:mixing a solution of the PVDF with a dispersion of the BT@polydopamine filler to obtain a mixture, and coating the mixture and drying to produce the film.

5. The method according to claim 4, wherein the dispersion of the BT@polydopamine filler is prepared by a process comprising:dispersing the BT@polydopamine filler in a polar organic solvent,wherein the dispersing is conducted under ultrasound and magnetic stirring that are conducted circularly.

6. The method according to claim 4, wherein the mixing comprises: adding the solution of the PVDF to the dispersion of the BT@polydopamine filler, subjecting a resulting mixture to vacuuming, and then standing under sealing.

7. A composite film, comprising a first polymethyl methacrylate (PMMA) film, a film, and a second PMMA film that are stacked sequentially, wherein the film is the film according to any one of claims 1 to 3 or the film prepared by the method according to any one of claims 4 to 6.

8. A method for preparing the composite film according to claim 7, comprising the following steps:subjecting a first PMMA solution to first coating and first drying to form the first PMMAfilm;mixing the solution of the PVDF with the dispersion of the BT@polydopamine filler to obtain a mixed solution, coating the mixed solution on the first PMMA film, and drying to form the film; and5 subjecting a second PMMA solution to second coating and second drying on the film to form the second PMMA film, obtaining the composite film.

9. The method according to claim 8, wherein the first drying, the drying, and the second drying each are conducted independently at a temperature of 50° C to 70 °C independently for 3 10 min to 8 min;after the second drying, the method further comprises: subjecting a resulting composite film to a third drying to obtain the composite film; andthe third drying is conducted at a temperature of 60 °C to 80 °C for 20 h to 26 h.15 10. Use of the film according to any one of claims 1 to 3, the film prepared by the methodaccording to any one of claims 4 to 6, the composite film according to claim 7, or the composite film prepared by the method according to any one of claims 8 to 9 in an energy storage capacitor.Application No: GB2419009.2Examiner: James HoggClaims searched: 1-10Date of search: 23 May 2025Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-2, 4-5 CN 110314250 A (UNIV JIANGXI SCI &TECHNOLOGY) See WP1 Accession abstract no. 2019-87393T. X 1,4-5 CN 118638329 A (UNIV NORTHWESTERN POLYTECHNICAL) See WPI accession abstract no. 2024-A0849X. X 1-2 Composites Science and Technology, vol. 118, 2015, Li Yuhan et al., Towards suppressing loss tangent: Effect of polydopamine coating layers on dielectric properties of core-shell barium titanate filled polyvinylidene fluoride composites, pages 198-206. See section 2.2-2.

3. X 1 Smart Materials and Structures, vol. 31, no. 11, 2022, Meng Qingyu et al., Piezoelectric performance improvement via macromolecular rearrangement, page 115012. See section 3.3 v A 1 Composites Science and Technology, vol. 186, 2019, Pu Yongping et al., Strong non-volatile voltage control of magnetization and the magnetodielectric properties in polymer-based sandwich-structured composites, page 107931. See section 2.2-2.3Categories:X Document indicating lack of novelty or inventive step A Document indicating technological background and or state of the art. Y Document indicating lack of inventive step if combined with one or more other documents of same category'. P Document published on or after the declared priority date but before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO &US patent documents classified in the following areas of the UKCX :Intellectual Property Office is an operating name of the Patent OfnceInternational Classification:Subclass Subgroup Valid From C08J 0003 / 205 01 / 01 / 2006 C08J 0005 / 18 01 / 01 / 2006 C08K 0003 / 01 01 / 01 / 2018 C08K 0007 / 16 01 / 01 / 2006Intellectual Property Office is an operating name of the Patent Ofnce

Images