An ultrahigh voltage thin film energy storage capacitor with low temperature drift

Abstract

The present application relates to a kind of ultra-high pressure film energy storage capacitor with low temperature drift.The capacitor core is stacked and wound by single-sided multi-string metallized polypropylene film and single-sided multi-string metallized polyester film;The thickness of polypropylene film dpp, the thickness of polyester film dpet and the temperature drift of capacitor satisfy the following relationship: {(ε pp / d pp )*α pet +(ε pet / d pet )*α pp} / {(ε pp / d pp ) + (ε pet / d pet )}≤+50 ppm / ℃.The advantage of the present application is that by combining polyester film with positive temperature difference coefficient and polypropylene film with negative temperature difference coefficient, and using special formula to prepare polypropylene film dielectric material, the dielectric loss at high temperature can be effectively reduced, the stability of capacity is improved, and by controlling the thickness of polyester film and polypropylene film, the prepared film energy storage capacitor can withstand ultra-high pressure.

Description

Technical Field

[0001] This invention relates to the field of thin-film energy storage capacitor technology, and specifically to an ultra-high voltage thin-film energy storage capacitor with low temperature drift. Background Technology

[0002] Polypropylene film energy storage capacitors are electronic components that use polypropylene film as the dielectric and aluminum foil or metallized film as the electrodes. They are wound and encapsulated with epoxy resin. These capacitors have technical characteristics such as low loss, high insulation resistance, strong overvoltage resistance, and excellent dielectric strength. Polypropylene film has high electric field strength, which can be used to produce ultra-high voltage film energy storage capacitor products.

[0003] Because the dielectric constant of polypropylene, the dielectric material in polypropylene film capacitors, changes with temperature, the increased thermal motion of dielectric molecules and the resulting changes in intermolecular forces cause capacitance fluctuations. This leads to temperature drift issues in existing metallized polypropylene film energy storage capacitors (such as the CBB / CL series). The capacitance becomes unstable with temperature changes, primarily affected by the temperature coefficient of the dielectric constant and thermal stress. In conventional applications (-40℃ to +85℃), the temperature drift is approximately ±2-5%, while capacitance stability is particularly critical in precision circuits such as energy buffers. This invention provides an ultra-high voltage film energy storage capacitor with low temperature drift. Through improvements in materials and structure, the temperature drift problem of film energy storage capacitors is mitigated to adapt to complex environmental changes, and while enhancing capacitance stability, the film capacitor can withstand ultra-high voltage. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an ultra-high voltage thin-film energy storage capacitor with low temperature drift, which can solve the problem of unstable capacitance of metallized polypropylene thin-film energy storage capacitors with temperature change in the prior art.

[0005] To solve the above technical problems, the technical solution of the present invention is: an ultra-high voltage thin film energy storage capacitor with low temperature drift, comprising a capacitor core, characterized in that: the capacitor core is formed by stacking and winding single-sided multi-string metallized polypropylene film and single-sided multi-string metallized polyester film. The thickness of the polypropylene film should meet the following requirement: d pp ≥V breakdown / E pp-breakdown The thickness of the polyester film should meet d. pet ≥V breakdown / E pet-breakdown , where V breakdown For target pressure resistance, E pp-breakdown E represents the breakdown field strength of the polypropylene film. pet-breakdown For the breakdown field strength of polyester film, d pp d represents the thickness of the polypropylene film. pet The thickness of the polyester film; The thickness d of the polypropylene film pp With polyester film thickness d pet The following relationship should be satisfied between them: (ε) pp / d pp )* |α pp |≈ (ε pet / d pet )* α pet , where α pp α is the temperature coefficient of polypropylene film. pet ε is the temperature coefficient of the polyester film. pp ε is the dielectric constant of the polypropylene film. pet Let d be the dielectric constant of the polyester film, and let d be the thickness of the polypropylene film. pp Polyester film thickness d pet The following relationship exists between the temperature drift of the capacitor and the temperature drift of the capacitor: {(ε pp / d pp )* α pet +(ε pet / d pet )* α pp} / {(ε pp / d pp ) + (ε) pet / d pet ≤+50 ppm / ℃; The thin-film energy storage capacitor prepared based on the above-obtained thickness ratio of polypropylene film to polyester film exhibits a temperature drift of ≤±1.2% in an environment of -40℃ to 105℃, and can withstand ultra-high voltage of 15-25KV.

[0006] Furthermore, the single-sided multi-strand metallized polypropylene film and the single-sided multi-strand metallized polyester film are alternately stacked and then wound, with the film layer and the metal layer being single-layered and spaced apart.

[0007] Furthermore, the polypropylene film is modified by adding 5-6 wt% of high-temperature resistant inorganic filler, and the high-temperature resistant inorganic filler is added to the polypropylene raw material by ultrasonic dispersion.

[0008] Furthermore, the high-temperature resistant inorganic filler is a mixture of surface-modified nano-alumina and nano-titanium dioxide. The nano-alumina is surface-modified by grafting maleic anhydride onto polypropylene, and the nano-titanium dioxide is surface-modified by titanate coupling agent. The mass ratio of surface-modified nano-alumina to surface-modified nano-titanium dioxide is 3:1-2.

[0009] Furthermore, the polyester film is a BOPET film.

[0010] Furthermore, during the heat setting of the capacitor core, the capacitor core is heated to 130-150°C in a vacuum or inert gas environment to eliminate internal stress and stabilize dimensions and electrical performance.

[0011] The advantages of this invention are as follows: By compositing a polyester film with a positive temperature coefficient and a polypropylene film with a negative temperature coefficient, dielectric loss at high temperatures can be effectively reduced, and capacity stability can be improved. Furthermore, by controlling the thickness of the polyester and polypropylene films, the prepared thin-film energy storage capacitor can withstand ultra-high voltages of 15KV-25KV. Simultaneously, by using a surface-modified nano-alumina and nano-titanium dioxide inorganic filler composite to modify the polypropylene film, and by preparing the polypropylene film dielectric material using a special formula, dielectric loss at high temperatures can be effectively reduced, and the dielectric constant is less affected by temperature, directly reducing the temperature drift of the thin-film energy storage capacitor and improving stability. The temperature drift is ≤±1.2% in an environment of -40℃ to 105℃. Through improvements in materials and structure, the temperature drift of the thin-film energy storage capacitor is effectively reduced to adapt to complex environmental changes. While improving the capacity stability of the thin-film energy storage capacitor, it also ensures that the thin-film energy storage capacitor can withstand ultra-high voltages, and improves the heat resistance and long-term reliability of the thin-film energy storage capacitor. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the stacked structure of a single-sided multi-string metallized polypropylene film and a single-sided multi-string metallized polyester film for a capacitor core according to Embodiment 1 of the present invention. Figure 2 The graph shows the relationship between capacitance and temperature at a frequency of 1 kHz for the thin-film energy storage capacitor prepared in Example 1 of the present invention and the thin-film energy storage capacitor of Comparative Example 1. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments will enable those skilled in the art to more fully understand this invention, but do not limit the invention to the scope of these embodiments.

[0014] Example 1: like Figure 1 As shown, the specific embodiment adopts the following technical solution: an ultra-high voltage thin-film energy storage capacitor with low temperature drift, including a capacitor core, which is formed by stacking and winding a single-sided multi-string metallized polypropylene film 1 and a single-sided multi-string metallized polyester film 2; the stacking method of the capacitor core is: the single-sided multi-string metallized polypropylene film 1 and the single-sided multi-string metallized polyester film 2 are alternately stacked and then wound, and the film layer and the metal layer are single-layered and spaced apart.

[0015] The thickness of the polypropylene film should meet d.pp ≥V breakdown / E pp-breakdown The thickness of the polyester film should meet d. pet ≥V breakdown / E pet-breakdown , where V breakdown For target pressure resistance, E pp-breakdown E represents the breakdown field strength of the polypropylene film. pet-breakdown For the breakdown field strength of polyester film, d pp d represents the thickness of the polypropylene film. pet The thickness of the polyester film; Polypropylene film thickness d pp With polyester film thickness d pet The following relationship should be satisfied between them: (ε) pp / d pp )* |α pp |≈ (ε pet / d pet )* α pet , where α pp α is the temperature coefficient of polypropylene film. pet ε is the temperature coefficient of the polyester film. pp ε is the dielectric constant of the polypropylene film. pet Let d be the dielectric constant of the polyester film, and d be the thickness of the polypropylene film. pp Polyester film thickness d pet The following relationship exists between the temperature drift of the capacitor and the temperature drift of the capacitor: {(ε pp / d pp )* α pet +(ε pet / d pet )* α pp} / {(ε pp / d pp ) + (ε) pet / d pet ≤+50 ppm / ℃; The thin-film energy storage capacitor prepared according to the above-obtained thickness ratio of polypropylene film 11 to polyester film 21 has a temperature drift of ≤±1.2% in an environment of -40℃~105℃ and can withstand ultra-high voltage of 15-25KV.

[0016] Among them, polyester film 21 is BOPET film.

[0017] During the heat setting of capacitor cores, the capacitor cores are heated to 130-150℃ in a vacuum or inert gas environment to eliminate internal stress and stabilize dimensions and electrical performance.

[0018] The polypropylene film 11 has a thickness of 7.5 μm; the polyester film 21 has a thickness of 10 μm and a capacitance of 15 nF, with 28 individual capacitors connected in series.

[0019] Individual voltage calculation: Total voltage (V) total Designed for 25kV, number of units in series (n): 28, each unit withstands a voltage (V). unit ): 25kV / 28≈893V; The breakdown electric field strength of BOPET film is approximately 400-500 MV / m; the breakdown electric field strength of polypropylene film is approximately 600 MV / m. Design safety margin: The design electric field strength of high voltage film capacitors is usually taken as 1 / 3 to 1 / 5 of the material breakdown field strength to ensure long-term reliability, and a conservative value of 1 / 4 is taken.

[0020] Typical breakdown field strength E of the material bd Safety design field strength E design For E bd / 4, Theoretical minimum thickness required to withstand voltage d=V / E design , Minimum thickness of polypropylene (PP): d: 893 / 150 ≈ 6.0μm Minimum thickness of polyester (PET) d: 893 / 100 ≈ 8.9μm The selected 7.5μm PP film fully meets the withstand voltage requirement at 893V (7.5μm * 150MV / m = 1125V>893V) and has a margin of about 26%, which is a reasonable choice. Similarly, the theoretical minimum thickness of PET film is about 9μm. Considering process fluctuations and long-term aging, a 10μm PET film is selected.

[0021] Temperature compensation ratio calculation: When two materials are connected in parallel, the total capacitance change is the weighted sum of the capacitance changes of each material.

[0022] PP temperature coefficient α pp ≈ -200 ppm / ℃, PET temperature coefficient α pet ≈ +300 ppm / ℃; Let the capacitance per unit area of ​​the PP layer be C. pp =ε pp / d pp The PET layer is C pet = ε pet / d pet To make the total temperature drift close to zero, the following must be satisfied: (C pp * |α pp |) ≈ (C pet * αpet ).

[0023] Substitute the dielectric constant ε pp ≈2.2, ε pet ≈3.2 and thickness d pp =7.5μm, d pet =10μm, C pp = 2.2 / 7.5 ≈ 0.293, C pet = 3.2 / 10 = 0.320, the contribution weights of the two are close, and the overall temperature drift α total = C pp *α pp +C pet *α pet / C pp +C pet The overall temperature drift was calculated to be approximately +60.9 ppm / ℃.

[0024] This means that by using a combination of 7.5μm PP + 10μm PET, the theoretical overall temperature drift will be significantly improved from -200ppm / ℃ for PP to a mere +60.9 ppm / ℃, with a very obvious compensation effect.

[0025] When the temperature change ΔT = 100℃, the total temperature drift is 0.609%, which is less than 1.2%.

[0026] Example 2: This second embodiment is the same as the first embodiment in the rest, except that the thickness of the polypropylene film 11 is 8.0 μm and the thickness of the polyester film 21 is 10 μm. The overall temperature drift is calculated to be approximately +68.9 ppm / ℃.

[0027] When the temperature change ΔT = 100℃, the total temperature drift is 0.689%, which is less than 1.2%.

[0028] Example 3: This third embodiment is the same as the rest of the first embodiment, except that the thickness of the polypropylene film 11 is 7.5 μm and the thickness of the polyester film 21 is 9.0 μm. The overall temperature drift is calculated to be approximately +74.0 ppm / ℃.

[0029] When the temperature change ΔT = 100℃, the total temperature drift is 0.740%, which is less than 1.2%.

[0030] Example 4: This fourth embodiment is the same as the rest of the first embodiment, except that the thickness of the polypropylene film 11 is 8.0 μm and the thickness of the polyester film 21 is 9.0 μm, and the overall temperature drift is calculated to be approximately +81.9 ppm / ℃.

[0031] When the temperature change ΔT = 100℃, the total temperature drift is 0.819%, which is less than 1.2%.

[0032] Example 5: This fifth embodiment is the same as the rest of the first embodiment, except that: 5-6 wt% of high-temperature resistant inorganic filler is added to the polypropylene film 11 for modification, and the high-temperature resistant inorganic filler is added to the polypropylene raw material by ultrasonic dispersion, with a power of 50-500 W and a time of 10-60 minutes.

[0033] The high-temperature resistant inorganic filler is a mixture of surface-modified nano-alumina and nano-titanium dioxide. The nano-alumina is surface-modified by maleic anhydride-grafted polypropylene (PP-g-MAH). During modification, the nano-alumina and PP-g-MAH are melt-mixed in a twin-screw extruder. High temperature and shear force are used to promote interfacial reaction. The modification temperature is 185℃, and the amount of PP-g-MAH is 10% of the mass of nano-alumina. After modification with PP-g-MAH, the surface of nano-alumina is wrapped by PP segments, forming a steric hindrance effect, reducing agglomeration, and improving dispersibility. Through chemical bonding and physical encapsulation, the interfacial adhesion is significantly improved and stress concentration is reduced.

[0034] Nano-titanium dioxide was surface modified using a titanate coupling agent, TC-201, at a concentration of 3.5% of the nano-titanium dioxide mass. The modification time was 60 minutes, the modification temperature was 45℃, and the pH value was 5.2. The titanate coupling agent bonded to the hydroxyl groups on the surface of nano-titanium dioxide through chemical bonds, forming a stable organic monolayer. This significantly improved the dispersibility of nano-titanium dioxide in organic media, reduced agglomeration, and enhanced its compatibility with organic polymers.

[0035] The mass ratio of surface-modified nano-alumina to surface-modified nano-titanium dioxide is 3:1-2.

[0036] Specifically, in this fifth embodiment, 5 wt% of high-temperature resistant inorganic filler is added, and the mass ratio of surface-modified nano-alumina to surface-modified nano-titanium dioxide is 3:1.

[0037] The large specific surface area of ​​nanofillers induces significant interfacial polarization at the polypropylene matrix interface, thereby increasing the dielectric constant. Uniformly dispersed inorganic nanoparticles can serve as physical crosslinking points, restricting the thermal motion of polypropylene molecular chains at high temperatures and reducing the influence of their conformational changes on the dielectric constant, thus reducing the temperature coefficient (absolute value). After modification with different coupling agents, both types of fillers can enhance the interfacial bonding with the PP matrix. At the same time, the introduced nanofillers form a large number of deep-level charge traps in the matrix, effectively suppressing conductivity loss and leakage current at high temperatures, making the dielectric properties more stable at high temperatures.

[0038] The temperature coefficient α of the modified polypropylene film pp ≈ -180 ppm / ℃, dielectric constant ε pp ≈2.7, the overall temperature drift is calculated to be approximately +45.9 ppm / ℃.

[0039] This means that by adding 5 wt% of high-temperature resistant inorganic filler to modify polypropylene film, the theoretical overall temperature drift will be significantly improved from -200 ppm / ℃ to a mere +45.9 ppm / ℃. Compared to before modification, there is a significant compensation effect, and the temperature drift of the capacitor is closer to 0.

[0040] When the temperature change ΔT = 100℃, the total temperature drift is 0.459%, which is less than 1.2%.

[0041] Comparative Example 1: Currently, the theoretical temperature drift of conventional polypropylene film energy storage capacitors on the market is -200ppm / ℃. When the temperature change ΔT=100℃, the total temperature drift is 2%, which is greater than 1.2%.

[0042] The relationship between capacitance and temperature at a frequency of 1 kHz is as follows for the thin-film energy storage capacitor prepared in Example 1 and the thin-film energy storage capacitor in Comparative Example 1. Figure 2 As shown in the figure, the green dashed line represents the relationship between capacitance and temperature of the conventional polypropylene film energy storage capacitor of Comparative Example 1, the orange solid line represents the relationship between capacitance and temperature of the conventional polyester film energy storage capacitor, and the blue solid line represents the relationship between capacitance and temperature of the film energy storage capacitor prepared in Example 1. It can be seen that the temperature drift of the film energy storage capacitor prepared in Example 1 is around 0, while the temperature drift of the conventional polypropylene film energy storage capacitor of Comparative Example 1 reaches 2%. The film capacitor of Example 1 has a lower temperature drift and improved stability.

[0043] This specific embodiment effectively reduces dielectric loss at high temperatures and improves capacity stability by compositing a polyester film with a positive temperature coefficient and a polypropylene film with a negative temperature coefficient. Furthermore, by controlling the thickness of the polyester and polypropylene films, the prepared thin-film energy storage capacitor can withstand ultra-high voltages of 15KV-25KV. Simultaneously, the polypropylene film is modified using a surface-modified nano-alumina and nano-titanium dioxide inorganic filler composite. By employing a special formula to prepare the polypropylene film dielectric material, dielectric loss at high temperatures is effectively reduced, and the dielectric constant is less affected by temperature, directly reducing the temperature drift of the thin-film capacitor and improving stability. The temperature drift is ≤±1.2% in an environment of -40℃ to 105℃. Through improvements in materials and structure, the temperature drift of the thin-film energy storage capacitor is effectively reduced to adapt to complex environmental changes, and while improving the capacity stability of the thin-film energy storage capacitor, it ensures that the thin-film energy storage capacitor can withstand ultra-high voltages.

[0044] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. An ultra-high voltage thin-film energy storage capacitor with low temperature drift, comprising a capacitor core, characterized in that: The capacitor core is formed by stacking and winding single-sided multi-string metallized polypropylene film and single-sided multi-string metallized polyester film. The thickness of the polypropylene film should meet the following requirement: d pp ≥V breakdown / E pp-breakdown The thickness of the polyester film should meet d. pet ≥V breakdown / E pet-breakdown , where V breakdown For target pressure resistance, E pp-breakdown E represents the breakdown field strength of the polypropylene film. pet-breakdown For the breakdown field strength of polyester film, d pp d represents the thickness of the polypropylene film. pet The thickness of the polyester film; The thickness d of the polypropylene film pp Polyester film thickness d pet The following relationship exists between the temperature drift of the capacitor and the temperature drift of the capacitor: {(ε pp / d pp )* α pet +(ε pet / d pet )* α pp } / {(ε pp / d pp ) + (ε) pet / d pet ) ≤ +50 ppm / ℃, where α pp α is the temperature coefficient of polypropylene film. pet ε is the temperature coefficient of the polyester film. pp ε is the dielectric constant of the polypropylene film. pet The dielectric constant of the polyester film; The thin-film energy storage capacitor prepared based on the above-obtained thickness ratio of polypropylene film to polyester film exhibits a temperature drift of ≤±1.2% in an environment of -40℃ to 105℃, and can withstand ultra-high voltage of 15-25KV.

2. The ultra-high voltage thin-film energy storage capacitor with low temperature drift according to claim 1, characterized in that: The single-sided multi-strand metallized polypropylene film and the single-sided multi-strand metallized polyester film are alternately stacked and then wound, with the film layer and the metal layer being single-layered and spaced apart.

3. The ultra-high voltage thin-film energy storage capacitor with low temperature drift according to claim 1, characterized in that: The polypropylene film is modified by adding 5-6 wt% of high-temperature resistant inorganic filler, and the high-temperature resistant inorganic filler is added to the polypropylene raw material by ultrasonic dispersion.

4. The ultra-high voltage thin-film energy storage capacitor with low temperature drift according to claim 3, characterized in that: The high-temperature resistant inorganic filler is a mixture of surface-modified nano-alumina and nano-titanium dioxide. The nano-alumina is surface-modified by grafting maleic anhydride onto polypropylene, and the nano-titanium dioxide is surface-modified by titanate coupling agent. The mass ratio of surface-modified nano-alumina to surface-modified nano-titanium dioxide is 3:1-2.

5. The ultra-high voltage thin-film energy storage capacitor with low temperature drift according to claim 1, characterized in that: The polyester film is a BOPET film.

6. The ultra-high voltage thin-film energy storage capacitor with low temperature drift according to claim 1, characterized in that: During the heat setting of the capacitor core, the capacitor core is heated to 130-150°C in a vacuum or inert gas environment to eliminate internal stress and stabilize dimensions and electrical performance.

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