A bt@so / pvdf composite material with different coating angles and a preparation method thereof

Abstract

The application discloses a BaTiO3@SiO2 / PVDF (BT@SO / PVDF) composite material with different coating angles and a preparation method thereof. The preparation method comprises the following steps: firstly, different coating angle BT@SO ceramic particles are obtained by controlling the relative content of cetyltrimethylammonium bromide and tetraethyl orthosilicate in a hydrolysis method; and then, the BT@SO ceramic particles are compounded with a PVDF matrix to obtain the BT@SO / PVDF composite material with different coating angles. The application can alleviate the negative correlation between the dielectric constant and the breakdown electric field to different degrees by using the different coating angles, and finally obtain a nano composite material with a high polarization value, a high breakdown field strength, a high energy density and high stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of dielectric composite material preparation, and particularly relates to a BT@SO / PVDF composite material with different coating angles and a preparation method thereof. BACKGROUND

[0002] At present, the storage and conversion equipment of electric energy mainly includes batteries, electrochemical supercapacitors and dielectric capacitors. The battery is an electric energy storage and conversion equipment with the highest energy density, but the power density of the battery is low (<500 W / kg), and the battery can only be applied to the field with low discharge speed requirement (>100 s). The electrochemical supercapacitor has moderate energy density and power density (10-10 6 W / kg), but the electrochemical supercapacitor has poor voltage resistance and is mainly used in the scene with fast discharge speed (<0.01 s). Compared with the above two, the dielectric capacitor has the highest power density (~10 8 W / kg), and in addition, the dielectric capacitor has the advantages of fast discharge speed, good stability, low cost and long service life, so that the dielectric capacitor has been widely concerned and applied and developed. In addition, according to the requirements of use conditions and environment, electronic devices are increasingly miniaturized and lightened, and higher requirements are put forward for the energy storage performance and processing performance of the capacitor.

[0003] In principle, the calculation method of the discharge energy density (U dis ) of the dielectric capacitor is as follows: U dis =∫EdD, wherein E is an applied electric field, and D is an electric displacement. For a linear dielectric, U dis can also be expressed as the formula: wherein ε0 and ε r respectively represent the vacuum dielectric constant (8.85×10 -12 F / m) and the relative dielectric constant of the dielectric, and in addition, E b represents the breakdown field of the dielectric. It can be seen from the above formula that the discharge energy density can be improved by increasing the breakdown field strength and the dielectric constant of the material, and it should be noted that the breakdown field strength is more obvious for improving the discharge energy density.

[0004] The common method at present stage is to mix ceramic filler and polymer matrix, and high energy storage density is realized by combining the high dielectric constant of ceramic filler and the high breakdown field strength of polymer, but in the BaTiO3 / PVDF-based nanocomposite, because the difference between the dielectric constant of ceramic filler and polymer matrix is too large, when BaTiO3 contacts and approaches, it is easy to realize the transfer of electric charge, and a local conductive path is formed, resulting in large material leakage current, and the main reason for this phenomenon is that the difference between the dielectric constant of ceramic filler and polymer matrix is too large, so that the electric field distribution of the composite material is uneven. In order to solve the above problems, many researchers can modify the surface of barium titanate (BaTiO3) by constructing a suitable core-shell structure, introduce a buffer layer, and generally use the method of modifying inorganic fillers with organic modifiers to improve the interface interaction. Silica is an insulating material with wide band gap, high breakdown strength and ultra-low dielectric loss, so SiO2 is coated on the surface of BaTiO3 as a coating. However, there are many problems, for example, coating SiO2 with good insulation on the surface of ceramic filler may reduce the polarization value of the composite material, and the energy storage density of the nanocomposite is limited. SUMMARY

[0005] In view of the deficiencies of the prior art, the first object of the present application is to provide a preparation method of different coating angle BT@SO / PVDF composite material with different coating angles. The preparation method of the present application can realize the shielding of the performance of the inner core BaTiO3 to different degrees by changing the coating angle of the surface of the ceramic filler, and then composite with polymer PVDF, and the different coating angles can alleviate the negative correlation between dielectric constant and breakdown field to different degrees, and finally obtain a nanocomposite with high polarization value, high breakdown field strength, high energy density and high stability.

[0006] The second object of the present application is to provide a different coating angle BT@SO / PVDF composite material with different coating angles prepared by the above preparation method.

[0007] In order to achieve the above object, the technical scheme adopted by the present application is as follows:

[0008] The application discloses a preparation method of a BT@SO / PVDF composite material with different coating angles, and the method comprises the following steps: adding cetyltrimethylammonium bromide (CTAB) into a solution containing barium titanate particles to obtain a mixed solution A, adjusting the pH of the mixed solution A to alkaline to obtain a mixed solution B, adding tetraethyl orthosilicate into the mixed solution B to obtain a mixed solution C, carrying out a reaction, carrying out solid-liquid separation, carrying out heat treatment on the obtained solid phase to obtain BT@SO ceramic particles, and then carrying out compounding of the BT@SO ceramic particles and PVDF by means of a flow casting method to obtain the BT@SO / PVDF composite material with different coating angles, wherein the solid-liquid mass-volume ratio of the cetyltrimethylammonium bromide and the tetraethyl orthosilicate in the mixed solution C is 0.157-0.938 g: 0.6-1.2 mL, preferably 0.157-0.938 g: 0.6-1.2 mL, and further preferably 0.313-0.625 g: 1.2 mL.

[0009] The preparation method of the application firstly obtains the BT@SO ceramic particles with different coating angles by means of a hydrolysis method, and the inventor finds that the BT@SO ceramic particles with different coating angles can be obtained by controlling the relative content of the cetyltrimethylammonium bromide and the tetraethyl orthosilicate, and then the BT@SO / PVDF composite material with different coating angles can be obtained by compounding the BT@SO ceramic particles and the PVDF matrix.

[0010] Preferably, the particle size of the barium titanate particles in the solution containing the barium titanate particles is 40-100 nm.

[0011] Preferably, the barium titanate particles are added into water to obtain the solution containing the barium titanate particles, and the solid-liquid mass-volume ratio of the barium titanate and water in the solution containing the barium titanate particles is 0.3-0.5 g: 90-150 mL.

[0012] Preferably, the mass ratio of the barium titanate particles to the cetyltrimethylammonium bromide is 0.25-0.5: 0.157-0.938, preferably 0.25-0.5: 0.157-0.938, and further preferably 0.5: 0.625.

[0013] Further preferably, when the mass ratio of the barium titanate particles to the cetyltrimethylammonium bromide is 0.5: 0.625, the solid-liquid mass-volume ratio of the cetyltrimethylammonium bromide to the tetraethyl orthosilicate in the mixed solution C is 0.625 g: 1.2 mL.

[0014] The solid-liquid mass-volume ratio of the cetyltrimethylammonium bromide to the tetraethyl orthosilicate is controlled within the above range, and finally the BT@SO / PVDF composite material with a 180° coating angle can be obtained.

[0015] Further preferably, the mass ratio of the barium titanate particles to cetyltrimethylammonium bromide is 0.5:0.313, and the solid-liquid mass-volume ratio of cetyltrimethylammonium bromide to tetraethyl orthosilicate in the mixed solution C is 0.313 g:1.2 mL.

[0016] The solid-liquid mass-volume ratio of cetyltrimethylammonium bromide to tetraethyl orthosilicate is controlled within the above range, and finally the BT@SO / PVDF composite material with a 90° coating angle can be obtained.

[0017] Preferably, ammonia water is added to adjust the mixed solution A to be alkaline.

[0018] Preferably, the stirring is performed for more than 12 h after the addition of tetraethyl orthosilicate to ensure sufficient stirring.

[0019] Preferably, the temperature of the heat treatment is 500-600°C, and the heat treatment holding time is 2-3 h.

[0020] The inventors have found that controlling the heat treatment temperature within the above range can sufficiently remove residual organic solvent molecules and simultaneously achieve good sintering of the ceramic particles.

[0021] Preferably, the BT@SO ceramic particles are added to N,N-dimethylformamide to obtain a dispersion liquid, PVDF is added to the dispersion liquid, and the stirring is performed at 40-50°C for more than 24 h to obtain a slurry. The slurry is coated on the surface of a glass plate, and the obtained thin film is dried to obtain a BT@SO / PVDF composite material with different coating angles.

[0022] The application also provides a BT@SO / PVDF composite material prepared by the preparation method. The BT@SO / PVDF composite material is composed of a PVDF matrix and BT@SO ceramic particles with different coating angles dispersed in the PVDF matrix. In the BT@SO ceramic particles, the coating angle of SiO2 to BaTiO3 is 90-360°, preferably 90-180°, and further preferably 90° or 180°.

[0023] Preferably, in the BT@SO ceramic particles with different coating degrees, the thickness of SiO2 is 30-50 nm.

[0024] Preferably, in the BT@SO / PVDF composite material, the mass fraction of BT@SO is 0.5-2 wt%, and preferably 0.5-1 wt%.

[0025] The preparation method of the application can controllably obtain the BT@SO / PVDF composite material with different coating angles, and the inventors find that the shielding effect of SiO2 with different coating angles on the core BaTiO3 is different, so that the dielectric constant under the same condition is as follows: 90° BaTiO3@SiO2 / PVDF > 180° BaTiO3@SiO2 / PVDF > 360° BaTiO3 / PVDF.

[0026] The greater the coating angle of the core BaTiO3, the more effectively the dielectric mismatch phenomenon caused by the too large difference in dielectric constant between the ceramic filler and the polymer matrix can be relieved, so that under the same content of the filler, the breakdown field strength of the 360° BaTiO3@SiO2 / PVDF nanocomposite is the highest, the 180° BaTiO3@SiO2 / PVDF is the second, and the 90° BaTiO3@SiO2 / PVDF is the lowest.

[0027] Comprehensive measurement, the 180° BaTiO3@SiO2 / PVDF has high breakdown field strength and high electric displacement value, which makes it have higher energy density than the 90° and 360° BaTiO3@SiO2 / PVDF. The 0.5wt% 180° BaTiO3@SiO2 / PVDF nanocomposite can obtain an energy density of up to 20.64J / cm 3 under an electric field strength of 650MV / m, and maintain an efficiency of 54.55%.

[0028] The beneficial results of the application are:

[0029] The application utilizes a simple hydrolysis reaction to produce a 30-50nm thick SiO2 coating layer on the surface of the 50nm barium titanate particles according to different coating angles, and then the ceramic filler and PVDF are compounded to prepare a nanocomposite material with high dielectric constant, high breakdown field strength and high energy density.

[0030] If the surface of the ceramic particles is not coated, the breakdown field strength will be greatly reduced due to the dielectric mismatch between the filler and the polymer, and on the contrary, if the surface of the ceramic particles is fully coated, the polarization strength of the nanocomposite material will inevitably be reduced. By coating the BT ceramic filler to different degrees, the polarization strength and breakdown strength of the nanocomposite material are maintained at a high level, so that a nanocomposite material with excellent comprehensive energy storage performance is obtained. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is the XRD graph of the BT@SO ceramic particles with different coating angles.

[0032] Figure 2 is the TEM graph of the BT@SO ceramic particles coated at 90°.

[0033] Figure 3 TEM image of BT@SO ceramic particles with 180° coating.

[0034] Figure 4 TEM image of BT@SO ceramic particles with 360° coating.

[0035] Figure 5 Dielectric constant, dielectric loss at different frequencies and dielectric constant and loss at 1 kHz as a function of filler content for 90° BaTiO3@SiO2 / PVDF nanocomposites.

[0036] Figure 6 Dielectric constant, dielectric loss at different frequencies and dielectric constant and loss at 1 kHz as a function of filler content for 180° BaTiO3@SiO2 / PVDF nanocomposites.

[0037] Figure 7 Dielectric constant, dielectric loss at different frequencies and dielectric constant and loss at 1 kHz as a function of filler content for 360° BaTiO3@SiO2 / PVDF nanocomposites.

[0038] Figure 8 Energy density, energy storage efficiency and maximum energy density and the corresponding electric field as a function of filler content for 90° BaTiO3@SiO2 / PVDF nanocomposites.

[0039] Figure 9 Energy density, energy storage efficiency and maximum energy density and the corresponding electric field as a function of filler content for 180° BaTiO3@SiO2 / PVDF nanocomposites.

[0040] Figure 10 Energy density, energy storage efficiency and maximum energy density and the corresponding electric field as a function of filler content for 360° BaTiO3@SiO2 / PVDF nanocomposites. DETAILED DESCRIPTION

[0041] Example 1

[0042] Preparation of 90° coating angle BT@SO ceramic particles: 0.5 g of barium titanate particles was added to 150 ml of deionized water, mixed thoroughly, and then 0.313 g of cetyltrimethylammonium bromide (CTAB) was added according to the required coating angle, and it was mixed thoroughly by ultrasonic. After mixing thoroughly, 7.5 ml of ammonia water was added to create a basic environment suitable for reaction, and finally 1.2 ml of tetraethyl orthosilicate was added and stirred thoroughly. After stirring, it was washed with deionized water and alcohol, dried in a 70°C oven, and then placed in a 500°C tube furnace for 2h to obtain 90° BT@SO ceramic particles.

[0043] Preparation of 90° coating angle BT@SO / PVDF nanocomposite film: In the preparation process, no BT@SO ceramic particles were added, and the mass fraction of BT@SO ceramic particles in the nanocomposite film was 0.5wt%, 1.0wt%, 1.5wt%, and 2.0wt%, respectively. Different amounts of BT@SO ceramic particles were prepared.

[0044] First, (4.5-x) g of N,N-dimethylformamide was added, then x g of 90° BT@SO ceramic particles was added according to the mass fraction of the prepared filler, and it was mixed thoroughly by ultrasonic. Finally, 0.5 g of PVDF was added and stirred at 50°C for 24h. After stirring, it was evenly coated on the surface of a glass plate, and then dried in a 70°C oven to obtain different coating angle BT@SO / PVDF nanocomposite films.

[0045] 90° BaTiO3@SiO2 / PVDF nanocomposites can achieve high electric displacement strength due to the small angle of the outer SiO2 layer, but at the same time, the breakdown field strength is at a low level. Therefore, the energy storage density and energy storage efficiency of pure PVDF, 0.5wt%, 1.0wt%, 1.5wt%, and 2.0wt% 90° BaTiO3@SiO2 / PVDF nanocomposites were (7.9 J / cm 3 ; 46.2%), (17.3 J / cm 3 ; 52.5%), (13.3 J / cm 3 ; 50.0%), (8.0 J / cm 3 ; 41.8%), (5.6 J / cm 3 ; 40.4%).

[0046] Example 2

[0047] Preparation of 180° coating angle BT@SO ceramic particles: 0.5 g of barium titanate was added to 150 ml of deionized water and mixed thoroughly, then 0.625 g of CTAB was added according to the required coating angle, and it was mixed thoroughly by ultrasonic, after it was mixed thoroughly, 7.5 ml of ammonia water was added to create a suitable alkaline environment for the reaction, finally 1.2 ml of tetraethyl orthosilicate was added and stirred thoroughly, after stirring was completed, it was washed thoroughly with deionized water and alcohol, dried in a 70°C oven, and then placed in a 500°C tube furnace for heat treatment to obtain 180° BT@SO ceramic particles.

[0048] Preparation of 180° coating angle BT@SO / PVDF nanocomposite film:

[0049] First, (4.5-x) g of N,N-dimethylformamide was added, then x g of 180° BT@SO ceramic particles was added according to the mass fraction of the prepared filler, and it was mixed thoroughly by ultrasonic, finally 0.5 g of PVDF was added and stirred at 50°C for 24 h. After stirring was completed, it was uniformly coated on the surface of a glass plate, then dried in a 70°C oven to obtain a 180° BT@SO / PVDF nanocomposite film.

[0050] Performance data:

[0051] 180° BaTiO3@SiO2 / PVDF not only combines the advantages of high electric displacement of 90° BaTiO3@SiO2 / PVDF, but also combines the advantages of high breakdown field strength of 360° BaTiO3@SiO2 / PVDF, and finally obtains the optimal energy storage performance. The energy storage density and energy storage efficiency of 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt% 180° BaTiO3@SiO2 / PVDF nanocomposites are (20.6 J / cm 3 ; 54.6%), (13.2 J / cm 3 ; 52.3%), (9.1 J / cm 3 ; 47.9%), (6.8 J / cm 3 ; 43.3%).

[0052] Example 3

[0053] Preparation of 360° coating angle BT@SO ceramic particles: 0.5 g of barium titanate was added to 150 ml of deionized water and mixed thoroughly, then 0.938 g of CTAB was added according to the required coating angle, and it was mixed thoroughly by ultrasonic, after it was mixed thoroughly, 7.5 ml of ammonia water was added to create a suitable alkaline environment for the reaction, finally 1.2 ml of tetraethyl orthosilicate was added and stirred thoroughly, after stirring was completed, it was washed thoroughly with deionized water and alcohol, dried in a 70°C oven, and then placed in a 500°C tube furnace for heat treatment to obtain 360° BT@SO ceramic particles.

[0054] Preparation of 360° wrapping angle BT@SO / PVDF nanocomposite film:

[0055] Firstly, (4.5-x) g of N, N-dimethylformamide was added, then x g of 360° BT@SO ceramic particles was added according to the mass fraction of the prepared filler, and then it was fully mixed by ultrasonic, finally 0.5 g of PVDF was added and stirred at 50°C for 24 h. After stirring, it was evenly coated on the surface of the glass plate, and then dried in a 70°C oven to obtain a 360° BT@SO / PVDF nanocomposite film.

[0056] Performance data:

[0057] The 360° complete wrapping of the BaTiO3 core with low dielectric constant and wide band gap SiO2 can effectively shield the performance of BaTiO3, so that the polarization strength of 360° BaTiO3@SiO2 / PVDF nanocomposite decreases, but 360° BaTiO3@SiO2 nanofiller can more effectively reduce the leakage current density of nanocomposite and alleviate the degree of electric field distortion, which can significantly improve the breakdown field strength of nanocomposite. The energy storage density and energy storage efficiency of 0.5wt%, 1.0wt%, 1.5wt%, 2.0wt% 360° BaTiO3@SiO2 / PVDF nanocomposite are (16.8J / cm 3 ;51.7%),(11.6J / cm 3 ;44.7%),(9.4J / cm 3 ;43.4%),(8.3J / cm 3 ;43.2%)。

[0058] Dielectric composite material performance test: a metal mask plate with a circular hole radius of 1 mm and a hole center distance of 4 mm was designed, and the metal mask plate was square with a side length of 30 mm. The pressed dielectric composite material was sandwiched between two metal mask plates, and gold electrodes were sputtered on the upper and lower surfaces. The upper and lower surfaces were sputtered at a power of 120 W for 140 s to ensure that the gold electrode had sufficient thickness.

Claims

1. A method for preparing BT@SO / PVDF composite materials with different coating angles, characterized by: The barium titanate particles are added into water to obtain a solution containing barium titanate particles, wherein the solid-liquid mass-volume ratio of barium titanate to water is 0.3-0.5 g: 90-150 mL.

2. The preparation method of the BT@SO / PVDF composite material with different coating angles according to claim 1, characterized in that: The particle size of the barium titanate particles in the solution containing barium titanate particles is 40-100 nm.

3. The preparation method of the BT@SO / PVDF composite material with different coating angles according to claim 1, characterized in that: The barium titanate particles are added into water to obtain a solution containing barium titanate particles, wherein the solid-liquid mass-volume ratio of barium titanate to water is 0.3-0.5 g: 90-150 mL.

4. The preparation method of the BT@SO / PVDF composite material with different coating angles according to any one of claims 1-3, characterized in that: The mass ratio of the barium titanate particles to cetyltrimethylammonium bromide is 0.25-0.5: 0.157-0.

938.

5. The preparation method of the BT@SO / PVDF composite material with different coating angles according to any one of claims 1-3, characterized in that: The mixture A is adjusted to alkaline by adding ammonia.

6. The preparation method of the BT@SO / PVDF composite material with different coating angles according to any one of claims 1-3, characterized in that: The stirring is performed for more than 12 h after adding tetraethyl orthosilicate.

7. The preparation method of the BT@SO / PVDF composite material with different coating angles according to any one of claims 1-3, characterized in that: The temperature of the heat treatment is 500-600 DEG C, and the heat treatment holding time is 2-3 h.

8. The preparation method of the BT@SO / PVDF composite material with different coating angles according to any one of claims 1-3, characterized in that: The BT@SO ceramic particles are added into N,N-dimethylformamide to obtain a dispersion liquid, PVDF is added into the dispersion liquid, and the stirring is performed at 40-50 DEG C for more than 24 h to obtain a slurry, the slurry is coated on the surface of a glass plate, and the obtained film is dried to obtain the BT@SO / PVDF composite material with different coating angles.

9. The BT@SO / PVDF composite material prepared by the preparation method of any one of claims 1-8, characterized in that: The BT@SO / PVDF composite material is composed of a PVDF matrix and BT@SO ceramic particles with different coating angles dispersed in the PVDF matrix, and the coating angle of SiO2 to BaTiO3 in the BT@SO ceramic particles is 90-360 DEG. 10.The BT@SO / PVDF composite material of claim 9, characterized in that: The thickness of SiO2 in the BT@SO ceramic particles with different coating angles is 30-50 nm. The mass fraction of BT@SO in the BT@SO / PVDF composite material is 0.5-2 wt%.

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