Full-fat cyclic polyimide film with improved high-temperature energy storage performance

Abstract

The application discloses a full aliphatic ring polyimide film with improved high-temperature energy storage performance, which is characterized by the following steps: completely removing aromatic ring to cut off the continuous conjugate path, combining the steric hindrance effect of non-coplanar aliphatic ring units, weakening the inter-chain pi-pi interaction and charge transfer complex (CTC) formation, thereby significantly widening the band gap; the film has a characteristic breakdown field strength of not less than 470 MV / m at 200 DEG C, a discharge energy density of not less than 3.3 J / cm3 at 90% efficiency, and good self-healing ability; compared with full aromatic polyimide, the high-temperature insulation stability and energy storage performance of the film are greatly improved; compared with semi-aromatic polyimide, the wide band gap design is more thorough; by optimizing the AIPI-1 (CPDA-DCHM) structure, the application realizes the best synergy of wide band gap and moderate chain accumulation density, overcomes the defect that the simple pursuit of large band gap width leads to loose structure and decreased breakdown performance, and is suitable for the field of 200-250 DEG C high-temperature film capacitors.

Description

Technical Field

[0001] This invention belongs to the field of polymer dielectric materials technology, specifically relating to a fully cyclic polyimide film with improved high-temperature energy storage performance, its preparation method and application, and particularly a fully cyclic polyimide film with excellent breakdown strength, high energy storage density and good self-healing properties under high-temperature conditions. Background Technology

[0002] With the rapid development of power electronics, new energy vehicles, and aerospace, the demand for film capacitors that can operate stably at temperatures of 200°C or even higher is becoming increasingly urgent. Polyimide (PI) has become an ideal candidate material for high-temperature energy storage dielectrics due to its excellent heat resistance and insulation properties. However, traditional fully aromatic polyimides (such as Kapton PI) contain continuous aromatic and imide rings in their molecular chains, forming a strong π-π conjugated system and charge transfer complex (CTC) effect, resulting in a narrow bandgap. Under high temperature and high field conditions, the leakage current increases sharply, and the energy storage density and efficiency decrease significantly.

[0003] To improve its performance, researchers attempted to introduce alicyclic units into the semi-aromatic polyimide system to weaken conjugation. However, the residual aromatic rings still prevented the complete elimination of interchain interactions, resulting in limited improvement in high-temperature insulation performance. Therefore, there is an urgent need to develop a novel polyimide dielectric material that can fundamentally solve the problem of conduction loss at high temperatures while maintaining good processability and mechanical strength. Summary of the Invention

[0004] The present invention aims to provide a fully alicyclic polyimide film with improved high-temperature energy storage performance. By completely removing the aromatic structure and introducing non-coplanar alicyclic units, a synergistic balance between wide bandgap, weak inter-chain interactions and appropriate chain packing density is achieved.

[0005] To achieve the above objectives, the present invention provides a fully alicyclic polyimide film whose molecular backbone does not contain aromatic ring structures, and whose polymer monomers are fully alicyclic dianhydrides and fully alicyclic diamines, wherein at least one monomer contains a non-coplanar alicyclic unit. The characteristic breakdown field strength (E0) of this film at 200 °C is... b The discharge energy density is not less than 470 MV / m, and at 200 ℃ and 90% charge-discharge efficiency, it is not less than 3.3 J / cm³.

[0006] Preferably, the band gap (E) of the full-cycloaliphatic polyimide is... g (5.0 eV) glass transition temperature (T) g (Higher than 530 K)

[0007] More preferably, the full-cycloaliphatic polyimide is selected from the following two specific structures: (1) AIPI-1 obtained by polymerization of cyclopentanetetracarboxylic dianhydride (CPDA) and 4,4'-dicyclohexylmethanediamine (DCHM); (2) AIPI-2 obtained by polymerization of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA) and 4,4'-dicyclohexylmethanediamine (DCHM).

[0008] The present invention also provides a method for preparing the thin film, comprising the following steps: (1) under an inert atmosphere, dissolving a fully alicyclic diamine monomer in a polar aprotic organic solvent and stirring until completely dissolved to obtain a diamine solution; (2) under low temperature ice-water bath conditions, adding a fully alicyclic dianhydride monomer in batches to the diamine solution and stirring continuously to produce a polycondensation reaction to prepare a polyamic acid precursor solution; (3) after degassing the polyamic acid precursor solution, uniformly coating it onto the substrate surface and performing gradient thermal imidization treatment to remove the solvent and complete the cyclization reaction; (4) cooling and peeling to obtain a fully alicyclic polyimide base film, which is then cut to obtain the target energy storage film.

[0009] Preferably, the molar ratio of the percyclocyclic diamine monomer to the percyclocyclic dianhydride monomer is the same.

[0010] Preferably, the thermal imidization process is as follows: under inert gas protection, the temperature is increased from room temperature to 250-300 ℃ at a rate of 25 ℃ / min, and held at that temperature for 1-3 hours; the aprotic polar solvent is N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc) or N,N-dimethylformamide (DMF).

[0011] The present invention further provides the application of the full-cycloaliphatic polyimide film in the preparation of high-temperature film capacitors at 200-250 °C.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: Significantly improved high-temperature energy storage performance: The all-alicyclic structure completely cuts off the main chain conjugated path, greatly widening the bandgap (>5.0 eV), effectively suppressing charge transfer and conduction losses under high temperature and high field conditions. For example, AIPI-1 achieves a discharge energy density of 4.71 J / cm³ at 200 ℃ and 90% efficiency, far superior to the traditional Kapton PI.

[0013] The balance between bandgap width and structural compactness has been optimized: this invention proposes that a larger Eg is not necessarily better. A comparison of AIPI-1 and AIPI-2 reveals that while excessively increasing the free volume (as in AIPI-2) can further weaken inter-chain interactions, loose packing reduces the breakdown field strength. AIPI-1 achieves the best synergy between a wide bandgap and moderate chain packing compactness, exhibiting optimal overall energy storage performance.

[0014] Excellent self-healing ability: the self-healing parameters of the film of this invention With a strength between 0.75 and 0.80, it can self-heal through localized ablation of the metal electrodes after breakdown, avoiding catastrophic device failure and improving the reliability of high-temperature operation. Attached Figure Description

[0015] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0016] Figure 1 This is a diagram illustrating the intrinsic decoupling mechanism of the all-aromatic-semi-alicyclic-all-alicyclic compounds provided in the embodiments of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0018] Comparative Example: Kapton PI Fully Aromatic Polyimide Film

[0019] Commercial Kapton PI film (manufactured by DuPont, model 100HN, approximately 25 micrometers thick) was used as a comparative example. Its bandgap width E... g = 2.31 eV, glass transition temperature T g = 584.70 K, chain spacing 3.30 Å, free volume fraction 15.26%. Breakdown field strength E at 200 °C. b = 316 MV / m, discharge energy density at 90% charge / discharge efficiency is 0.29 J / cm³; at 250 ℃, E b = 213 MV / m, with a discharge energy density of 0.037 J / cm³ at 90% efficiency.

[0020] Example 1: Preparation of AIPI-1 (CPDA-DCHM) full-cycle polyimide film

[0021] Step 1: Monomer purification and drying Cyclopentanetetracarboxylic dianhydride (CPDA, purity ≥98%) was dried in a vacuum oven at 120 °C for 12 hours and set aside for later use. 4,4'-Dicyclohexylmethanediamine (DCHM, purity ≥99%) was dried under nitrogen protection at 60 °C for 6 hours and set aside for later use. N-Methylpyrrolidone (NMP, chromatographic grade) was soaked in a 4 Å molecular sieve for 24 hours to remove water, controlling the moisture content to be below 50 ppm.

[0022] Step 2: Polymerization reaction to prepare polyamic acid precursor solution In a 100 mL three-necked flask equipped with a mechanical stirrer, nitrogen inlet, and thermometer, 4.12 g (20 mmol) of DCHM and 40 mL of anhydrous NMP were added. Under a nitrogen atmosphere, the mixture was stirred at room temperature (25 ± 1 °C) until the DCHM was completely dissolved, yielding a clear, transparent solution. The reaction flask was placed in an ice-water bath to lower the internal temperature to 0–5 °C. With vigorous stirring, 4.48 g (20 mmol) of CPDA was added in three batches (approximately 1.4 g each), 15 minutes apart. After the addition was complete, the ice-water bath was removed, and the reaction mixture was allowed to return to room temperature naturally. The reaction was continued under nitrogen protection with stirring for 24 hours, yielding a yellow, transparent, viscous polyamic acid (PAA) solution with a solid content of 15 wt%. Infrared spectroscopy was used to monitor the characteristic peak of the acid anhydride (1780 cm⁻¹) during the reaction. -1 and 1850 cm -1 The disappearance of ) and the characteristic peak of amyl acid (1650 cm⁻¹) -1 The appearance of ).

[0023] Step 3: Debubbling and Coating The obtained PAA solution was vacuum degassed in a vacuum drying oven at room temperature (25 °C) for 2 hours until no bubbles escaped from the solution surface. A clean glass substrate (100 mm × 100 mm) was ultrasonically cleaned sequentially with acetone, ethanol, and deionized water for 15 minutes, dried with nitrogen, and coated with a release agent (dilute dimethyl dichlorosilane solution). The degassed PAA solution was uniformly coated onto the glass substrate, and the wet film thickness was controlled by spin coating (spray coating parameters: low speed 300 rpm for 10 seconds, high speed 1500 rpm for 30 seconds). The final dry film thickness was approximately 20 μm.

[0024] Step 4: Gradient thermal imidization A glass substrate coated with a PAA wet film was placed in a tube furnace, and high-purity nitrogen gas (flow rate 1 L / min) was introduced to purge air. Thermal imidization was performed according to the following procedure: the temperature was increased from room temperature (25 °C) to 80 °C at a rate of 3 °C / min, and held for 30 minutes to slowly remove most of the solvent; then the temperature was increased to 150 °C at 3 °C / min and held for 30 minutes; finally, the temperature was increased to 280 °C at 3 °C / min and held for 2 hours to ensure complete imidization. The substrate was then allowed to cool naturally to room temperature, maintaining a nitrogen atmosphere throughout the process.

[0025] Step 5: Peeling and Cutting After cooling, the glass substrate was removed, and the film was immersed in deionized water for 10 minutes. The film was then gently peeled off using a release agent to obtain the AIPI-1 base film. The film was vacuum dried at 120 °C for 2 hours to remove surface-adsorbed moisture. It was then cut into the required size (e.g., circular pieces with a diameter of 2 cm for electrical performance testing) and stored in a desiccator for later use. The resulting AIPI-1 film had a thickness of 20 ± 1 μm and was colorless and transparent.

[0026] Performance test results: Bandgap width E g (Experimental value) 5.46 eV, T g = 538.51 K, interchain spacing 6.45 Å, free volume fraction 26.83%. Breakdown field strength E at 200 °C b = 565 MV / m, discharge energy density at 90% efficiency is 4.71 J / cm³; E at 250 ℃ b = 397 MV / m, discharge energy density at 90% efficiency is 1.63 J / cm³, self-healing parameter =0.750.

[0027] Example 2: Preparation of AIPI-2 (BTA-DCHM) full-acid cyclic polyimide film

[0028] Step 1: Monomer purification and drying Bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA, purity ≥97%) was dried in a vacuum oven at 100 °C for 12 hours. The drying treatment of 4,4'-dicyclohexylmethanediamine (DCHM) and N,N-dimethylacetamide (DMAc) was the same as in Example 1.

[0029] Step 2: Polymerization reaction In a nitrogen-protected 250 mL three-necked flask, 4.12 g (20 mmol) of DCHM and 50 mL of anhydrous DMAc were added. After dissolving by stirring at room temperature, the mixture was cooled to 0–5 °C in an ice-water bath. 5.24 g (20 mmol) of BTA was added in portions, with 20-minute intervals between each addition. After the addition was complete, the mixture was heated to room temperature and stirred for 24 hours to obtain a polyamic acid solution with a solid content of 15 wt%.

[0030] Step 3: Debubbling and Coating Similar to Example 1, the PAA adhesive was degassed under vacuum at room temperature for 2 hours. Using the same cleaning treatment on the glass substrate, the spin coating parameters were adjusted to a low speed of 300 rpm / 10 seconds and a high speed of 1200 rpm / 30 seconds to control the dry film thickness to approximately 20 μm.

[0031] Step 4: Thermal imidization The thermal imidization procedure was the same as in Example 1: the temperature was increased at 3 °C / min to 80 °C / 30 min, 150 °C / 30 min, and 280 °C / 2 h, under nitrogen protection.

[0032] Step 5: Peeling and Cutting Same as in Example 1, after cooling, the film was peeled off, vacuum dried at 120 °C for 2 hours, and then cut for later use. The resulting AIPI-2 film was 20 ± 1 μm thick and colorless and transparent.

[0033] Performance test results: E g = 5.35 eV, T g = 540.10 K, interchain spacing 6.64 Å, free volume fraction 29.23%. E at 200 ℃ b = 471 MV / m, discharge energy density at 90% efficiency is 3.31 J / cm³; E at 250 ℃ b =347 MV / m, discharge energy density at 90% efficiency is 1.22 J / cm³. Self-healing parameters = 0.794.

[0034] Example 3: CPDA-IPDA full-cycle polyimide film (isophorone diamine system)

[0035] Step 1: Individual Preparation Cyclopentanetetracarboxylic dianhydride (CPDA) was dried as in Example 1. Isophorone diamine (IPDA, a mixture of isomers, purity ≥99%) was purified by vacuum distillation at 80 °C under nitrogen protection, and specific fractions were collected for later use. The solvent NMP was used for dehydration as in Example 1.

[0036] Step 2: Polymerization reaction In a nitrogen-protected reaction flask, 3.40 g (20 mmol) of IPDA and 35 mL of anhydrous NMP were added and stirred at room temperature to dissolve. The mixture was then cooled to 0–5 °C in an ice-water bath, and 4.48 g (20 mmol) of CPDA was added in portions over a period of 45 minutes. The ice bath was removed, and the mixture was allowed to react at room temperature for 24 hours to obtain a pale yellow, transparent PAA solution with a solid content of approximately 16 wt%.

[0037] Step 3: Debubbling and Coating The PAA solution was degassed under vacuum at room temperature for 2.5 hours. After cleaning and coating the glass substrate with the release agent, a wet film was prepared using a blade coating method (blade gap 300 μm) to control the dry film thickness to approximately 20 μm.

[0038] Step 4: Thermal imidization Program: Increase temperature at 3 °C / min to 80 °C / 30 min → 150 °C / 30 min → 250 °C / 1 h → 300 °C / 1 h (the last step is to ensure complete imidization). Nitrogen flow rate: 1.5 L / min.

[0039] Step 5: Peeling and Post-processing After natural cooling, the film was immersed in deionized water for peeling and then vacuum dried at 120 °C for 2 hours. A colorless film with a thickness of 18~22 μm was obtained.

[0040] Estimated performance: E g The predicted value is >5.1 eV, and the interchain spacing and free volume are between AIPI-1 and AIPI-2. It is estimated that the discharge energy density at 200 ℃ and 90% efficiency is >3.5 J / cm³, and the self-healing performance is good.

[0041] Example 4: CBDA-DCHM full-ester cyclic polyimide film (cyclobutane dianhydride system)

[0042] Step 1: Individual Preparation 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA, purity ≥98%) was dried in a vacuum oven at 80 °C for 24 hours. The drying of DCHM and solvent DMAc was the same as in Example 2.

[0043] Step 2: Polymerization reaction Under nitrogen protection, 4.12 g (20 mmol) of DCHM was dissolved in 45 mL of anhydrous DMAc, and the solution was cooled to 0–5 °C in an ice-water bath. 3.92 g (20 mmol) of CBDA was added in portions of 1.0 g at 20-minute intervals. After the addition was complete, the solution was stirred at 0–5 °C for 2 hours, then slowly raised to room temperature. The total reaction time was 36 hours (due to the low activity of CBDA). A PAA solution with a solid content of approximately 15 wt% was obtained.

[0044] Step 3: Debubbling and Coating Vacuum degassing at room temperature for 3 hours. Coating was then performed on a glass substrate using spin coating (low speed 300 rpm / 10 s, high speed 1500 rpm / 40 s).

[0045] Step 4: Thermal imidization Because the imidization temperature of CBDA-type polyimide is relatively high, the program was adjusted as follows: increasing the temperature by 2 ℃ / min to 80 ℃ / 30 min → 120 ℃ / 30 min → 200 ℃ / 1 h → 320 ℃ / 2 h. Nitrogen protection was maintained throughout the process.

[0046] Step 5: Peeling and Cutting After cooling, the film adheres tightly to the glass substrate and needs to be soaked in warm water for 30 minutes before peeling. It is then vacuum dried at 120 ℃ for 2 hours and cut. The film thickness is 20±1 μm, and it is light yellow and transparent.

[0047] Estimated performance: T g Predicted value > 550 K, E g >5.2 eV. Excellent dimensional stability at high temperatures, suitable for applications requiring high thermomechanical properties.

[0048] Example 5: Copolymerized full-cycle polyimide film of CPDA / BTA mixed dianhydride and DCHM

[0049] Step 1: Preparation of mixed dianhydrides CPDA and BTA were gently ground and mixed evenly in a mortar in a molar ratio of 1:1 (10 mmol each, i.e., 2.24 g CPDA and 2.62 g BTA), and then dried in a vacuum oven at 100 °C for 12 hours. DCHM (20 mmol, 4.12 g) and NMP solvent were treated as described above.

[0050] Step 2: Polymerization reaction Under nitrogen protection, DCHM was dissolved in 50 mL of anhydrous NMP and cooled to 0–5 °C in an ice-water bath. The total amount of mixed dianhydrides, 4.86 g, was divided into five batches, with one batch added every 30 minutes. After the addition was complete, the mixture was allowed to rise naturally to room temperature and stirred for 30 hours to obtain a homogeneous PAA solution (random structure copolymer) with a solid content of 14 wt%.

[0051] Step 3: Debubbling and Coating Vacuum degassing for 2 hours. Film was then formed on a glass substrate using spin coating (parameters same as in Example 1).

[0052] Step 4: Thermal imidization Program: Increase temperature at 3 ℃ / min to 80 ℃ / 30 min → 150 ℃ / 30 min → 280 ℃ / 2 h. Nitrogen protection.

[0053] Step 5: Peeling and Post-processing Same as Example 1. The resulting film has a thickness of 20±2 μm, is colorless and transparent, and has better toughness than AIPI-1 and AIPI-2.

[0054] Performance regulation: Free volume fraction approximately 28%, interchain spacing approximately 6.5 Å. Breakdown field strength and energy storage density are between AIPI-1 and AIPI-2, with significantly improved film formation and flexibility.

[0055] Example 6: Preparation of AIPI-1 thin films using different thermal imidization processes

[0056] Steps 1-3: Prepare the same CPDA-DCHM PAA wet film as in Example 1 (monomer, polymerization, degassing, and coating steps are the same).

[0057] Step 4: Two-step thermal imidization The glass substrate coated with a PAA wet film was placed in a tube furnace, and high-purity nitrogen gas (flow rate 1 L / min) was introduced. The procedure is as follows: • Increase the temperature from room temperature to 80°C at a rate of 5°C / min and hold for 30 minutes; • Increase the temperature to 150℃ at a rate of 5℃ / min and hold for 30 minutes; • Increase the temperature to 250℃ at a rate of 5℃ / min and hold for 3 hours; • Increase the temperature to 300℃ at a rate of 2℃ / min and hold for 1 hour; • Allow to cool naturally to room temperature, with nitrogen protection throughout the process.

[0058] Step 5: Peeling and Post-processing Same as Example 1. The thickness of the obtained AIPI-1 film is 20 ± 1 μm.

[0059] Performance Comparison: Compared to Example 1, the film imidization is more complete (infrared detection 1775 cm⁻¹). -1 and 1710 cm -1 (characteristic peak ratio increased), T g The K value increased to approximately 542 K. At 200 °C, the breakdown field strength Eb was approximately 560 MV / m, and the 90% efficiency discharge energy density was approximately 4.68 J / cm³ (essentially the same as in Example 1). After 1000 hours of continuous aging at 200 °C and a 200 MV / m electric field, the insulation resistance retention rate increased by approximately 15%, indicating superior long-term high-temperature stability.

[0060] All the above embodiments have achieved the preparation of all-alicyclic polyimide films. The molecular dynamics calculations of the comparative examples and Examples 1 and 2 are shown in Table 1. The results show that its high-temperature energy storage performance is far superior to that of traditional aromatic polyimides, and it is suitable as a dielectric material for high-temperature film capacitors of 200~250 °C.

[0061] The foregoing has shown and described the basic principles, main features, and advantages of this invention. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this invention. Various changes and modifications can be made to this invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

[0062]

Claims

1. A fully cyclic polyimide film for improving high-temperature energy storage performance, characterized in that, The molecular backbone of the polycyclic polyimide does not contain an aromatic ring structure, and its polymer monomers are polycyclic dianhydrides and polycyclic diamines, wherein the polycyclic dianhydrides and / or polycyclic diamines contain non-coplanar alicyclic units. The characteristic breakdown field strength (Eb) of the thin film at 200 °C is not less than 470 MV / m, and the discharge energy density at 200 °C and 90% charge-discharge efficiency is not less than 3.3 J / cm³.

2. The allocycloaliphatic polyimide film for improving high-temperature energy storage performance according to claim 1, characterized in that, The full-cycloaliphatic polyimide has a band gap (Eg) greater than 5.0 eV and a glass transition temperature (Tg) higher than 530 K.

3. The allocyclopolyimide film for improving high-temperature energy storage performance according to claim 2, characterized in that, The full-cycloaliphatic polyimide is selected from any of the following structures: (a) AIPI-1 obtained by polymerization of cyclopentanetetracarboxylic dianhydride (CPDA) and 4,4'-dicyclohexylmethanediamine (DCHM); (b) AIPI-2 obtained by polymerization of bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA) and 4,4'-dicyclohexylmethanediamine (DCHM).

4. The allocyclopolyimide film for improving high-temperature energy storage performance according to claim 2, characterized in that, The thickness of the film is 10-30 micrometers; the characteristic breakdown field strength of the film at 250 °C is not less than 340 MV / m, and the discharge energy density at 250 °C and 90% charge-discharge efficiency is not less than 1.2 J / cm³.

5. The allocyclopolyimide film for improving high-temperature energy storage performance according to claim 4, characterized in that, The self-healing parameters of the thin film Calculated by the following formula: in, , , , and These represent the number of C, N, H, F, and O atoms in the polymer repeating unit, respectively, and the thin film... The value is between 0.75 and 0.

80.

6. The allocyclopolyimide film for improving high-temperature energy storage performance according to claim 5, characterized in that, The film has a free volume fraction (FFV) of 25%-30% and a chain spacing of 6.0-7.0 Å.

7. A method for preparing a fully cyclic polyimide film with improved high-temperature energy storage performance according to any one of claims 1 to 6, characterized in that, Includes the following steps: (1) Under an inert atmosphere, the per-alicyclic diamine monomer is dissolved in a polar aprotic organic solvent and stirred until completely dissolved to obtain a diamine solution; (2) Under low temperature ice-water bath conditions, the per-alicyclic dianhydride monomer is added to the diamine solution in batches and stirred continuously to produce a polycondensation reaction to prepare a polyamic acid precursor solution; (3) After degassing the polyamic acid precursor solution, it is uniformly coated on the substrate surface and subjected to gradient thermal imidization treatment to remove the solvent and complete the cyclization reaction; (4) Cooling and peeling are used to obtain a per-alicyclic polyimide base film, which is then cut to obtain the target energy storage film.

8. The method for preparing a fully cyclic polyimide film with improved high-temperature energy storage performance according to claim 7, characterized in that, The molar ratio of the per-alicyclic diamine monomer to the per-alicyclic dianhydride monomer is the same.

9. The method for preparing a fully cyclic polyimide film with improved high-temperature energy storage performance according to claim 7, characterized in that, The thermal imidization process is as follows: under inert gas protection, the temperature is increased from room temperature to 250-300 ℃ at a rate of 25 ℃ / min and held for 1-3 hours; the aprotic polar solvent is N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc) or N,N-dimethylformamide (DMF).

10. The application of a fully cyclic polyimide film with improved high-temperature energy storage performance according to any one of claims 1 to 6 in a high-temperature film capacitor, characterized in that, The operating temperature of the high-temperature film capacitor is 200-250 ℃.

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