Polypropylene modification-based thin film capacitor, preparation method thereof and new energy vehicle

Abstract

The invention discloses a thin film capacitor based on polypropylene modification, a preparation method thereof and a new energy vehicle, and electrical performance and mechanical performance of the capacitor are improved by doping high dielectric constant and wide bandgap nanoparticles in a polypropylene matrix. And a sandwich structure design is adopted, and the high dielectric constant layer and the polypropylene film are compounded through a hot pressing process, so that the overall performance of the capacitor is enhanced. The plasma surface modification technology improves the surface energy of the polypropylene film, enhances the binding force with the aluminum metal layer, and improves the insulation characteristic and moisture resistance of the film. The mechanical property and the electrical property of the polypropylene film are optimized by the two-way stretching process, and the thickness uniformity and the dielectric property of the film are ensured. Through the improvements, the optimized thin film capacitor has higher stability and longer service life when being applied to the new energy vehicle, the thermal runaway risk is reduced, the energy storage efficiency is improved, meanwhile, the size and weight of the capacitor are reduced, and improvement of the overall performance of the new energy vehicle is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of film capacitors, and in particular to a film capacitor based on polypropylene modification, a preparation method thereof, and a new energy vehicle. Background Art

[0002] In the context of the rapid development of new energy vehicles, film capacitors, as key electronic components, play a vital role in the power system, charging system and energy recovery system of electric vehicles. Existing film capacitors widely use polypropylene as the insulating dielectric material. Thanks to its high dielectric strength, good dielectric constant and low loss factor, polypropylene has become a common choice in the capacitor market. In addition, the chemical stability and aging resistance of polypropylene enable it to perform well in high-frequency and large-capacity applications, meeting the high-performance requirements of new energy vehicles for capacitors.

[0003] However, with the advancement of new energy vehicle technology and the increasing requirements for capacitor performance, existing polypropylene film capacitors have shown limitations in thermal management and mechanical bonding. The relatively low thermal conductivity of polypropylene may lead to local hot spots inside the capacitor under high-load conditions, affecting the stability and life of the capacitor and possibly causing failure or damage. In addition, the mechanical bonding strength between polypropylene and the aluminum metal layer is insufficient, which may lead to separation between the electrode and the dielectric layer, affecting the performance and safety of the capacitor, especially in high-temperature or high-humidity vehicle environments. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a film capacitor based on polypropylene modification and a preparation method thereof, and a new energy vehicle to improve the above problems. The present invention improves the surface roughness of the aluminum metal layer, which not only enhances the bonding performance of the polypropylene film and the aluminum metal layer, but also effectively reduces the hot spot temperature expansion of the film capacitor, providing a more reliable solution for the application of high-performance film capacitors.

[0005] The present invention provides a method for preparing a film capacitor based on polypropylene modification, which comprises the following steps: S1: Matrix regulation: The first step in matrix regulation in a polypropylene matrix is ​​to select suitable nanoparticles, which include high dielectric constant nanoparticles and wide bandgap nanoparticles. By doping these nanoparticles into polypropylene, its electrical and mechanical properties can be significantly improved, providing new possibilities for the development of electronic devices such as capacitors. By regulating the polypropylene matrix and combining the doping of high dielectric constant and wide bandgap nanoparticles, a composite material with superior performance can be formed. The high dielectric constant nanoparticles are selected from barium titanate (BaTiO3), strontium titanate (SrTiO3) or barium strontium titanate (Ba x Sr 1-xThe wide bandgap nanoparticles are selected from one or more of titanium dioxide (TiO2), silicon dioxide (SiO2), aluminum oxide (Al2O3), magnesium oxide (MgO) or zinc oxide (ZnO).

[0006] S2: Structural optimization design: The two layers of high dielectric constant layers are compounded with the polypropylene film through a hot pressing process to enhance the overall performance of the capacitor; wherein the polypropylene film is arranged between the two layers of high dielectric constant layers to form a "sandwich" structure; the "sandwich" structure design of the polypropylene film is crucial to improving the overall performance of the film capacitor. The structure is formed by two layers of high dielectric constant material and a layer of polypropylene film in the middle. The high dielectric constant layer and the polypropylene film are efficiently compounded through adhesives, hot pressing, sputtering, deposition and other processes. In the design, it is necessary to precisely control the thickness of the high dielectric constant material layer and the performance of the polypropylene film to achieve the best electric field distribution and energy storage capacity. When using a hot pressing process for interlayer bonding, the setting of temperature and pressure is crucial to ensure good bonding between layers and the stability of the overall structure.

[0007] S3: Surface modification: By utilizing plasma modification technology, polar groups can be introduced on the surface of polypropylene film. This surface modification can improve the surface energy of polypropylene, improve adhesion and wettability, and thus promote bonding with other materials (such as coatings or adhesives). In addition, after plasma treatment, an inorganic coating can be deposited on the surface of the film. This layer of coating can not only improve the insulation properties of the material, but also enhance its resistance to moisture and chemical corrosion, and improve the working stability and service life of film capacitors in harsh environments.

[0008] S4: Process optimization: mainly focuses on controlling the stretching temperature and stretch ratio in the biaxial stretching process. The stretching process can significantly improve the mechanical properties and electrical properties of the polypropylene film. In this process, the stretching temperature needs to be accurately controlled to avoid thermal degradation of polypropylene, while also promoting the orientation of its molecular chains and improving the strength and rigidity of the film. In addition, optimizing the stretch ratio is also a factor that cannot be ignored. A suitable stretch ratio can improve the thickness uniformity and dielectric properties of the film. In particular, in the present invention, the stretching temperature is controlled at 80-120°C, and the stretch ratio is 3:1 to 5:1.

[0009] Through the above steps, the present invention can effectively improve the comprehensive performance of polypropylene-based film capacitors, making them perform particularly well in a variety of high-performance applications.

[0010] It should be noted that the preparation of the thin film capacitor may include some other necessary steps, which can be implemented according to existing technologies and will not be elaborated in detail in the present invention.

[0011] The embodiment of the present invention further provides a film capacitor, which is prepared by the above-mentioned method for preparing a film capacitor based on modified polypropylene.

[0012] Among them, the reactive power and equivalent resistance ESR of the capacitor are determined by calculating the total effective length of the electrodes at both ends of the film capacitor, the height of the polymer film, the height of the unmetallized edge, and the current and loss in the electrodes; Calculate the equivalent conductivity and dielectric constant by applying a potential difference and setting electrically insulating boundaries; Optimize thermal management of film capacitors by simulating the temperature distribution inside the film capacitors; The performance of film capacitors can be optimized by simulating the current density distribution on the electrode surface.

[0013] Among them, in the simulation process of calculating the equivalent conductivity and dielectric constant, the metallized electrode originally belonging to the next layer is retained on the boundary of the last layer, and the corresponding electric potential of the metallized electrode on the boundary is given in the process of setting the boundary conditions; the axial current density and average electric field strength in the film capacitor are expressed by the formula:

[0014]

[0015] In the formula, is the current, is the angular frequency, A sec is the axial cross-sectional area in m 2 Unit, E axial is the axial component of the electric field, in volts per meter, and V is the volume of the film capacitor, in m 3 ; Then the equivalent conductivity σ of the film capacitor is equ (ω) and dielectric constant Ɛ equ (ω) is:

[0016] ; in, is the dielectric constant of vacuum‌, and j is the imaginary unit.

[0017] Wherein, a film capacitor core having a high dielectric constant and good mechanical properties is formed by stacking and compounding a plurality of film layers; By disassembling the film capacitor core into its components, it is easy to analyze and optimize the capacitor's structure and performance.

[0018] An embodiment of the present invention further provides a new energy vehicle, which includes the above-mentioned film capacitor.

[0019] The embodiments of the present invention significantly improve the electrical and mechanical properties of the capacitor by doping high dielectric constant and wide bandgap nanoparticles into the polypropylene matrix. The "sandwich" structure design and plasma surface modification technology not only enhance the bonding performance of the polypropylene film and the aluminum metal layer, but also effectively reduce the hot spot temperature expansion of the film capacitor, thereby improving the thermal stability and reliability of the capacitor. The optimization of the biaxial stretching process further improves the mechanical and electrical properties of the film, ensures the thickness uniformity and dielectric properties of the film, and thus provides a more reliable and efficient capacitor solution for new energy vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a schematic diagram of the microstructure of the film capacitor core; FIG2 is a simplified boundary condition diagram of a film capacitor; Figure 3 is the temperature distribution diagram within the thin film stack structure; Figure 4 shows the current density distribution on the surface of the capacitor electrode; Figure 5 is a disassembled diagram of a film capacitor core; Figure 6 is a diagram showing the structure of a film capacitor core. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0023] Embodiment 1: First, let's introduce the battery preparation In this embodiment, barium titanate (BaTiO3) is used as the doping filler.

[0024] First, prepare the two main raw materials, polypropylene (PP) and barium titanate (BaTiO3). It is crucial to ensure the purity and quality of the raw materials to ensure the performance of the final product. PP and barium titanate are mixed in a predetermined ratio. This step usually uses a high-speed mixer to ensure that the two materials can be evenly dispersed. The uniformity of the mixing directly affects the effect of the subsequent melt extrusion, so the mixing time and speed need to be carefully controlled. The uniformly mixed materials are fed into the extruder. At high temperatures, the polypropylene will melt and mix thoroughly with the barium titanate to form a uniform composite material. In this process, the control of temperature and pressure is very important to avoid thermal degradation or decomposition of the material. After extrusion, the molten composite material needs to be cooled quickly to maintain its shape and properties. After cooling, the material is cut into small pellets for subsequent processing and molding. The size and uniformity of these pellets will affect the quality of subsequent molding. The pelletized composite material is processed into films or other parts of the desired shape using injection molding or compression molding technology.

[0025] Then, the BaTiO3 filler was dispersed into the adhesive chlorinated polypropylene (CPP) and coated onto the polypropylene film. The two coated polypropylene films were then hot pressed to prepare a sandwich structure with a high dielectric constant layer in the middle layer. In this structure, the middle layer effectively improves the dielectric constant, while the outer layer has high breakdown strength and low dielectric loss. The maximum discharge energy density of this multilayer film at 450V / ㎛ can reach 6.75 J / ㎤, and the charge and discharge efficiency is maintained at 79%.

[0026] Next, the aluminum metal is placed in a plasma treatment device, oxygen is selected to increase the hydrophilicity of the surface, and the gas pressure is usually in the range of 0.1-1 Torr; the power is generally set at 50-300 watts; the treatment time is generally between 0.5-5 minutes, depending on the desired effect. The surface energy is measured immediately after treatment to ensure that the aluminum metal layer surface is sufficiently active, usually greater than 50mN / m.

[0027] Finally, a biaxial stretching treatment is used, that is, before the polypropylene film is prepared, the polypropylene film is stretched using a biaxial stretching device. The temperature is set at 80-120°C, and the film is stretched in the longitudinal and transverse directions, respectively, with a stretching ratio of 3:1 to 5:1, to ensure that the film has good mechanical properties. After stretching, annealing is performed at a temperature of 120-140°C for 10-20 minutes to eliminate the stress inside the film and enhance its stability.

[0028] In this embodiment, a film capacitor can be prepared based on the annealed polypropylene film.

[0029] The following introduces the calculation of the working parameters of film capacitors.

[0030] First is the method to calculate conductivity and dielectric constant: Since the direction of applied voltage to the capacitor is fixed, only the electrical parameters along the axial direction need to be analyzed and tested. In theory, it is only necessary to apply a certain potential difference between the two sides of the axial direction and set the boundary in the stacking direction as electrical insulation, so as to obtain the distribution of current and potential in the stacked film. When simulating the complete capacitor winding, this setting is obviously reasonable. However, since only the innermost layer of all the windings of the capacitor is not in contact with the metallized electrode, the above boundary conditions cannot accurately reflect the electric field distribution inside the winding. Figure 1 As shown, during the simulation, the metallized electrodes originally belonging to the next layer are retained on the boundary of the last layer, and the corresponding electric potential is given to the metallized electrodes on the boundary during the process of setting the boundary conditions.

[0031] In this implementation, the accuracy of the electric field distribution and current density distribution is ensured by assigning the corresponding electric potential of the metallized electrode on the boundary in the boundary condition setting. The accuracy of these distributions directly affects the calculation of conductivity, dielectric constant, dielectric loss, power loss and equivalent resistance ESR. Therefore, the setting of boundary conditions is a key step in the entire calculation process, which ensures the accuracy of subsequent formula derivation and calculation.

[0032] Specifically, based on the above settings, a simplified thin film capacitor boundary condition diagram as shown in Figure 2 can be obtained. The axial current density and average electric field strength in the thin film capacitor can be expressed by the formula:

[0033]

[0034] Where A sec is the axial cross-sectional area in m 2 Unit, E axial is the axial component of the electric field, in volts per meter, and V is the volume of the film capacitor, in m 3 . And because:

[0035]

[0036] Therefore, the conductivity σ of the metallized film equivalent material is equ (ω) and dielectric constant Ɛ equ (ω) is:

[0037]

[0038] According to the above formula, the equivalent conductivity and dielectric constant can be calculated, where: is the dielectric constant of vacuum‌, and j is the imaginary unit.

[0039] Next is the formula for calculating dielectric loss and power loss: Assume that the total effective length of the electrodes at both ends of the capacitor is D, the height of the polymer film is H, and the height of the unmetallized edge is Hmer. In the electrode at the lower end, when the height Z is less than H-Hmer, the current in the electrode remains unchanged; when Z is greater than Hmer and less than H-Hmer, the current decreases linearly, and when Z is greater than H-Hmer, the current is 0. In summary, the current I in the lower electrode z and loss d pele It is expressed as follows:

[0040]

[0041] Integrate the loss on the lower electrode. Since the current and loss distribution in the upper electrode are symmetrical with the lower electrode, the total electrode loss can be calculated as:

[0042] The reactive power of the capacitor is:

[0043] Therefore the reactive power of the capacitor can be rewritten as follows:

[0044] Among them, T met is the thickness of the metallized electrode, is the density of the metallized electrode, T poly is the thickness of the polymer part, d z is the length of the capacitor in the height direction, C is the capacitance value, U is the voltage across the capacitor, is the dielectric constant of polypropylene film, f is the frequency, =2πf,I rms is the RMS current flowing in the capacitor.

[0045] The loss tangent of the film capacitor core of this embodiment 8×10 -4 , put it into the calculation, and the dielectric loss of the polymer film inside the capacitor can be obtained:

[0046] Taking into account the electrode and dielectric losses, the total internal loss P of the capacitor can be expressed as: .

[0047] Therefore, the equivalent resistance ESR can also be written as:

[0048] In this embodiment, further, Figure 3 As shown, the thermal management of the film capacitor can be optimized by simulating the temperature distribution inside the film capacitor.

[0049] Specifically, by simulating the temperature distribution inside the film capacitor, it can help identify local hot spots that may appear inside the capacitor, and then adjust the internal structure of the capacitor based on the simulation results, such as the electrode layout and the distribution of insulating materials, to optimize the heat flow path and reduce heat accumulation.

[0050] In this embodiment, further, Figure 4 As shown, the performance of the film capacitor can be optimized by simulating the current density distribution on the electrode surface.

[0051] Among them, by simulating the current density distribution on the electrode surface, the design of the electrode can be optimized according to the simulation results of the current density distribution, such as adjusting the shape and size of the electrode to reduce the problems of current concentration and electric field unevenness, thereby reducing the loss of the capacitor and improving its efficiency.

[0052] In this embodiment, further, Figure 5 As shown, the film capacitor core can be disassembled into multiple components to facilitate analysis and optimization of the capacitor's structure and performance.

[0053] In this embodiment, further, Figure 6 As shown, a film capacitor core with high dielectric constant and good mechanical properties can be formed by stacking and compounding multiple film layers.

[0054] The above are only preferred embodiments of the present invention, which are used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific embodiments. The protection scope of the present invention is not limited to the above embodiments, and all technical solutions under the concept of the present invention belong to the protection scope of the present invention.

Claims

1. A method for preparing a film capacitor based on polypropylene modification, characterized in that: The method comprises the following steps: S1, doping high dielectric constant nanoparticles and wide bandgap nanoparticles into a polypropylene matrix to obtain a polypropylene film; S2, compounding the two high dielectric constant layers with the polypropylene film by a hot pressing process; wherein the polypropylene film is arranged between the two high dielectric constant layers; S3, introducing polar groups on the surface of the polypropylene film by using plasma modification technology; S4, biaxially stretching and annealing the plasma-modified polypropylene film to prepare a film capacitor based on the annealed polypropylene film.

2. The method for preparing a film capacitor based on polypropylene modification according to claim 1, characterized in that: In step S1, the high dielectric constant nanoparticles are selected from one or more of barium titanate, strontium titanate or barium strontium titanate; the wide bandgap nanoparticles are selected from one or more of titanium dioxide, silicon dioxide, aluminum oxide, magnesium oxide or zinc oxide.

3. The method for preparing a film capacitor based on polypropylene modification according to claim 1, characterized in that: In step S2, the high dielectric constant layer and the polypropylene film are efficiently compounded by adhesive, hot pressing, sputtering, and deposition processes.

4. The method for preparing a film capacitor based on polypropylene modification according to claim 1, characterized in that: In step S3, the plasma modification technique includes treating the aluminum metal layer in oxygen plasma to increase the hydrophilicity of the surface.

5. The method for preparing a film capacitor based on polypropylene modification according to claim 1, characterized in that: In step S4, the stretching temperature of the biaxial stretching process is controlled at 80-120°C, and the stretching ratio is 3:1 to 5:1; the annealing temperature is set at 120-140°C, and the time is 10-20 minutes.

6. A film capacitor, characterized in that: The film capacitor is prepared by the method for preparing a polypropylene-modified film capacitor according to any one of claims 1 to 5.

7. The film capacitor according to claim 6, characterized in that: Determine the reactive power and equivalent resistance (ESR) of the capacitor by calculating the total effective length of the electrodes at both ends of the film capacitor, the height of the polymer film, the height of the unmetallized edge, and the current and loss in the electrodes; Calculate the equivalent conductivity and dielectric constant by applying a potential difference and setting electrically insulating boundaries; Optimize thermal management of film capacitors by simulating the temperature distribution inside the film capacitors; The performance of film capacitors can be optimized by simulating the current density distribution on the electrode surface.

8. The film capacitor according to claim 7, characterized in that: In the simulation process of calculating equivalent conductivity and dielectric constant, the metallized electrode originally belonging to the next layer is retained on the boundary of the last layer, and the corresponding electric potential of the metallized electrode on the boundary is assigned in the process of setting boundary conditions; wherein, the axial current density and average electric field strength in the film capacitor are expressed by the formula: In the formula, is the current, is the angular frequency, A sec is the axial cross-sectional area in m 2 Unit: E axial is the axial component of the electric field, in volts per meter, and V is the volume of the film capacitor, in m 3 ; Then the equivalent conductivity σ of the film capacitor is equ (ω) and dielectric constant Ɛ equ (ω) is: ； in, is the dielectric constant of vacuum‌, and j is the imaginary unit.

9. The film capacitor according to claim 6, characterized in that: By stacking and compounding multiple film layers, a film capacitor core with high dielectric constant and good mechanical properties is formed; By disassembling the film capacitor core into its components, it is easy to analyze and optimize the capacitor's structure and performance.

10. A new energy vehicle, characterized in that: A film capacitor comprising any one of claims 6 to 9.

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