Sequentially arranged polyimide copolymer for capacitors, its preparation method and applications

Abstract

The present invention discloses a sequentially arranged polyimide copolymer for a capacitor, its preparation method and application. The preparation method of the polyimide copolymer of the present invention comprises the following steps: Under stirring conditions, a solution of 4,4'-biphenylene ether dianhydride is dropped into a solution of a diamine monomer (one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, 4,4'-(1,4-phenylene diisopropylidene)dianiline), and stirring reaction is carried out; the molar ratio of 4,4'-biphenylene ether dianhydride to the diamine monomer is 1:2; hexafluorodiacid anhydride is added to the obtained solution, and stirring reaction is carried out; the obtained solution is dried to evaporate the solvent, heat-treated, and cooled to obtain a sequentially arranged polyimide copolymer for a capacitor. The polyimide copolymer of the present invention has a high glass transition temperature, a high breakdown strength and a high energy storage density, and still has a high charge-discharge efficiency and a low leakage current density at high temperatures, effectively improving the high-temperature performance of the capacitor.

Description

Technical Field

[0001] The present invention relates to the technical fields of high energy storage density organic dielectric thin film materials and capacitors, and particularly relates to an ordered polyimide copolymer for capacitors, a preparation method thereof, and an application thereof. Background Art

[0002] Dielectric thin film capacitors have been widely used in power electronic systems such as electric vehicles, grid-connected photovoltaic power generation, and oil exploration due to their advantages such as fast charge and discharge rates and high power density. Compared with inorganic ceramic materials, polymer dielectrics have become the preferred materials for thin film capacitors due to their low cost, easy processing, and high reliability. In recent years, with the increasing maturity of the third-generation semiconductor technology, power electronic devices are developing towards higher power and higher integration. However, the high-temperature working conditions brought about by high integration and high power density pose higher requirements for the heat resistance of thin film capacitors. Currently, the safe operating temperature of commercially available biaxially oriented polypropylene film (BOPP) is limited to 105 °C, and when the temperature gradually rises to 120 °C or above, the conductance loss and cumulative heat of BOPP show an exponential upward trend, resulting in a sharp decline in the charge and discharge efficiency, significantly increasing the failure probability of thin film capacitors, and thus seriously threatening the stability and safety of the entire power electronic system. Therefore, researchers are actively exploring and developing thin film materials for thin film capacitors suitable for high-temperature environments to solve the problem of the poor performance of commercial BOPP dielectrics under high-temperature conditions. Pure polymer materials can avoid problems such as filler dispersion and interfacial bonding, and show great potential in the large-scale production of high-performance polymer dielectrics. To improve the heat resistance of pure polymer thin film materials, researchers have adopted the strategy of designing highly conjugated structures. However, the insulation performance and thermal stability of materials are often mutually exclusive. To solve this contradiction, a series of norbornene polymers with non-conjugated structures and non-planar structures have been reported. However, in the face of extreme temperatures (>200 °C), the norbornene polymer thin film materials obtain high discharge energy density at the cost of sacrificing the charge and discharge efficiency, which means that they cannot meet the energy storage density requirements of thin film capacitors under extreme working conditions. Therefore, the development of pure polymer-based dielectric materials with both heat resistance and high energy storage performance is still the key research direction in this field.

[0003] In summary, the development of a new high-temperature resistant and high energy storage density pure polymer dielectric material is of great significance for improving the performance of polymer thin film capacitors and meeting the requirements of practical engineering applications. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an ordered polyimide copolymer for capacitors, a preparation method thereof, and an application thereof.

[0005] The technical solutions adopted by the present invention are as follows.

[0006] A sequentially arranged polyimide copolymer for a capacitor has the following structural formula:

[0007]

[0008] Wherein, X is selected from , , One of them. Correspond to the polymers co-PI ABAC , co-PI A’BA’C And co-PI A”BA”C .

[0009] Based on the design principle of balancing the thermal stability and electrical insulation of the material, the sequentially arranged polyimide copolymer for the capacitor is obtained by reacting a diamine monomer (one of 2,2-bis(4-aminophenyl)propane (denoted as diamine A), p-phenylenediamine (denoted as diamine A'), 4,4'-(1,4-phenylenediisopropylidene)dianiline (denoted as diamine A")), 4,4'-biphenylether dianhydride (denoted as dianhydride B), and hexafluorodiacid dianhydride (denoted as dianhydride C).

[0010] The preparation method of the above-mentioned sequentially arranged polyimide copolymer for a capacitor includes the following steps:

[0011] (1) Under stirring conditions, drop the 4,4'-biphenylether dianhydride solution into the diamine monomer solution and stir to react; the diamine monomer is one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine (denoted as diamine A'), 4,4'-(1,4-phenylenediisopropylidene)dianiline, and the molar ratio of 4,4'-biphenylether dianhydride to the diamine monomer is 1:2;

[0012] (2) Add hexafluorodiacid dianhydride to the solution obtained in step (1) and stir to react;

[0013] (3) Dry and evaporate the solvent of the solution obtained in step (2), perform high-temperature treatment, and cool to obtain the sequentially arranged polyimide copolymer for a capacitor.

[0014] The preparation method of the sequentially arranged polyimide copolymer for the capacitor of the present invention pre-polymerizes the diamine and different dianhydrides successively, then performs imidization reaction and high-temperature treatment, and is placed in cold water for demoulding and drying the moisture, thus obtaining the corresponding sequentially arranged polyimide copolymer for the capacitor.

[0015] Preferably, the solvent of the 4,4'-biphenylether dianhydride solution in step (1) is N-methylpyrrolidone (NMP), and the concentration is 0.025~0.25M;

[0016] Preferably, the solvent of the diamine monomer solution in step (1) is N-methylpyrrolidone, and the concentration is 0.05 - 0.5 M.

[0017] Preferably, the temperature of the stirring reaction in step (1) is room temperature (25 - 28 °C), and the time is 1 - 3 h.

[0018] Preferably, the molar ratio of hexafluorodiacid anhydride to diamine monomer in step (2) is (0.5 - 1.5):2.

[0019] More preferably, the molar ratio of hexafluorodiacid anhydride to diamine monomer is 1:2.

[0020] Preferably, the temperature of the stirring reaction in step (2) is room temperature (25 - 28 °C), and the time is 1 - 3 h.

[0021] Preferably, the hexafluorodiacid anhydride in step (2) is added in 2 - 3 portions.

[0022] Preferably, the drying temperature in step (3) is 80 - 90 °C, and the time is 12 - 16 h.

[0023] Preferably, the high-temperature treatment in step (3) is: reacting at 150 - 160 °C for 1 - 2 h, reacting at 200 - 210 °C for 1 - 2 h, and reacting at 250 - 260 °C for 1 - 2 h.

[0024] Preferably, the solution is poured onto a glass plate before drying in step (3).

[0025] Preferably, after cooling, it is immersed in cold water to separate the polyimide copolymer, and then dried.

[0026] More preferably, the drying temperature is 80 - 90 °C, and the time is 12 - 16 h.

[0027] The application of the polyimide copolymer arranged in sequence for capacitors in the preparation of high-temperature capacitors.

[0028] The polyimide copolymer arranged in sequence for capacitors of the present invention is mainly obtained by imidization reaction of a diamine monomer (one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, 4,4'-(1,4-phenylene diisopropylidene)dianiline), 4,4'-biphenylether dianhydride, and hexafluorodiacid anhydride. By controlling the molar ratio of the two different dianhydride monomers and the reaction sequence, the sequential arrangement effect of the polymer units is achieved. On the one hand, the ether bond in the dianhydride monomer 4,4'-biphenylether dianhydride can improve the E g , thus ensuring the electrical insulation performance of the material. At the same time, in order to balance the sacrifice brought by the flexible ether bond T gThe cost is thus reduced, and the dianhydride monomer hexafluorodiacid anhydride containing trifluoromethyl is introduced. By arranging two different polymer units in sequence, the contradiction between the heat resistance and electrical insulation properties of the material is alleviated. The sequentially arranged polyimide copolymer for capacitors of the present invention simultaneously has excellent heat resistance and high energy storage density, providing a strategy and direction for the design of polymer thin film capacitor materials for extreme working conditions. At the same time, the preparation process has extremely high operability, the raw materials are easily available, and it is suitable for industrial application. The material of the present invention can be used as the dielectric material of thin film capacitors for normal temperature and high temperature.

[0029] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0030] (1) The polyimide copolymer is obtained by the imidization reaction of commercially available diamine and dianhydride monomer in the present invention, which can stably work in a high-temperature environment of 200 °C and above, meeting the requirements of practical engineering applications for thin film capacitors.

[0031] (2) The sequentially arranged polyimide copolymer for capacitors of the present invention synergistically optimizes the heat resistance and electrical insulation properties of the material through the sequential arrangement of two different polyimide derivative units, breaking through the contradiction that the two properties are mutually exclusive in material design, and obtaining a high glass transition temperature, high breakdown strength and high energy storage density. Moreover, the process has strong operability, the raw materials are easily available, and it is suitable for large-scale industrial application.

[0032] (3) By optimizing the selection of monomers and through a specific controlled polymerization technique in the present invention, the target units are added one by one in a predetermined order, thereby formulating a polyimide copolymer (ABAC type) with a clear sequence structure. The sequential arrangement of two different units can avoid the formation of a long-distance conjugated structure formed by the introduction of flexible ether bonds, inhibit the formation of long-distance charge transfer complexes, hinder the migration of carriers, and keep the material still having a low leakage current density at high temperature and strong field.

[0033] (4) The sequentially arranged polyimide copolymer for capacitors of the present invention has a maximum charge-discharge density with a charge-discharge efficiency > 90% of up to 5.53 J cm -3 , and a breakdown resistance strength of up to 563 MV m -1 . Description of the Drawings

[0034] Figure 1 It is a schematic diagram of the preparation process of the sequentially arranged polyimide copolymer dielectric thin film material for capacitors in Example 1 of the present invention.

[0035] Figure 2 It is a graph of the thermal performance test results of 8 different PI-based polymer dielectric thin film materials.

[0036] Figure 3 It is a graph showing the test results of the dielectric properties of 8 different PI-based polymer dielectric thin film materials at 200 °C.

[0037] Figure 4 It is a graph showing the test results of the energy storage properties of 8 different PI-based polymer dielectric thin film materials at 200 °C.

[0038] Figure 5 It is a graph showing the test results of the breakdown of 8 different PI-based polymer dielectric thin film materials at 200 °C.

[0039] Figure 6 It is a graph showing the test results of the leakage current of 8 different PI-based polymer dielectric thin film materials at 200 °C. Detailed implementation manners

[0040] The technical solutions of the present invention will be further explained and illustrated below in conjunction with specific embodiments and the accompanying drawings.

[0041] Embodiment 1

[0042] A polyimide copolymer dielectric thin film material arranged in sequence for a capacitor, denoted as co-PI ABAC , and its preparation method includes the following steps (the preparation process is as Figure 1 shown):

[0043] (1) Dissolve 0.1129 g of diamine A (2,2-bis(4-aminophenyl)propane, 0.50 mmol) in 5 mL of NMP solution and stir at room temperature;

[0044] (2) During the stirring of the solution prepared in step 1, gradually add dropwise 5 mL of NMP solution in which 0.0774 g of dianhydride B (4,4'-biphenylene ether dianhydride, 0.25 mmol) is dissolved, and continue to stir at room temperature for 3 h;

[0045] (3) Continue to add 0.1098 g of dianhydride C (hexafluorodiacid anhydride, 0.25 mmol) powder to the above solution in 2-3 portions, and continue to stir at room temperature for 2 h;

[0046] (4) Pour the above mixed solution onto a glass plate of 50 mm×50 mm, and leave it standing in an 80 °C environment for 12 h to evaporate the NMP solvent;

[0047] (5) Transfer the glass plate to a heating box for high-temperature treatment. The high-temperature conditions are: react at 150 °C for 1 h, react at 200 °C for 1 h, and react at 250 °C for 1 h;

[0048] (6) Cool the glass plate after the reaction is complete to room temperature, and soak it in cold water to separate the copolymer dielectric thin film from the glass plate;

[0049] (7) Place the film detached from the glass plate in an 80 °C heating oven for 12 h to dry the excess moisture.

[0050] The thickness of the copolymer dielectric film material arranged in the above preparation is 8 - 10 μm, and both the length and width are 50 mm.

[0051] Example 2

[0052] A polyimide copolymer dielectric film material arranged in sequence for a capacitor, and its preparation method includes the following steps:

[0053] Dissolve 0.0671 g of p-phenylenediamine (denoted as diamine A') in 5 mL of NMP solution. After the powder is completely dissolved, add 5 mL of NMP solution in which 0.0963 g of 4,4'-biphenyl ether dianhydride (the molar ratio of diamine to dianhydride is 2:1) is dissolved to the solution. After stirring at room temperature for 3 h, continue to add 0.1366 g of hexafluorodiacid anhydride (0.31 mmol) powder to the above solution in 2 - 3 portions, and continue to stir for 2 h. The subsequent steps are the same as steps (4) - (7) of Example 1, denoted as co-PI A‘BA’C

[0054] Example 3

[0055] A polyimide copolymer dielectric film material arranged in sequence for a capacitor, and its preparation method includes the following steps:

[0056] Dissolve 0.1436 g of 4,4'-(1,4-phenylene diisopropylidene) diphenylamine (denoted as diamine A'') in 5 mL of NMP solution. After the powder is completely dissolved, add 5 mL of NMP solution in which 0.0646 g of 4,4'-biphenyl ether dianhydride (the molar ratio of diamine to dianhydride is 2:1) is dissolved to the solution. After stirring at room temperature for 3 h, continue to add 0.0918 g of hexafluorodiacid anhydride (0.21 mmol) powder to the above solution in 2 - 3 portions, and continue to stir for 2 h. The subsequent steps are the same as steps (4) - (7) of Example 1, denoted as co-PI A”BA”C

[0057] Comparative Example 1

[0058] A conventional PI-based polymer dielectric film material, and its preparation method includes the following steps:

[0059] Dissolve 0.1436 g of 4,4'-diaminodiphenyl ether in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1564 g of pyromellitic dianhydride to the solution (the molar ratio of the two is 1:1), and stir at room temperature for 4 h. The subsequent steps are the same as those in steps (4)-(7) of Example 1, denoted as regular PI.

[0060] Comparative Example 2

[0061] A PI-based polymer dielectric thin film material, and its preparation method includes the following steps:

[0062] Dissolve 0.1265 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1735 g of 4,4'-biphenyl ether dianhydride to the solution (the molar ratio of the two is 1:1), and stir at room temperature for 4 h. The subsequent steps are the same as those in steps (4)-(7) of Example 1, denoted as PI AB .

[0063] Comparative Example 3

[0064] A PI-based polymer dielectric thin film material, and its preparation method includes the following steps:

[0065] Dissolve 0.1019 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1981 g of hexafluorodiacid anhydride to the solution (the molar ratio of the two is 1:1), and stir at room temperature for 4 h. The subsequent steps are the same as those in steps (4)-(7) of Example 1, denoted as PI AC .

[0066] Comparative Example 4

[0067] A PI-based polymer dielectric thin film material, and its preparation method includes the following steps:

[0068] Dissolve 0.1507 g of 2,2-bis(4-aminophenyl)propane in 10 mL of NMP solution. After the powder is completely dissolved, add 0.1493 g of 1,2,4,5-cyclohexanetetracarboxylic dianhydride to the solution (the molar ratio of the two is 1:1), and stir at room temperature for 4 h. The subsequent steps are the same as those in steps (4)-(7) of Example 1, denoted as PI AD .

[0069] Comparative Example 5

[0070] A randomly copolymerized PI-based polymer dielectric thin film material, and its preparation method includes the following steps:

[0071] Dissolve 0.1129 g of 2,2-bis(4-aminophenyl)propane in 5 mL of NMP solvent. Dissolve 0.0774 g of 4,4'-biphenylene ether dianhydride and 0.1098 g of hexafluorodiacid anhydride in 5 mL of NMP solvent. After complete dissolution of both, add the NMP solution of the dissolved dianhydride to the solution of the dissolved diamine and stir at room temperature for 4 h. The subsequent steps are the same as those in steps (4)-(7) of Example 1, denoted as r-co-PI.

[0072] Performance Test

[0073] (1) The differential scanning calorimetry (DSC) results of the thin film samples prepared in Examples 1-3 and Comparative Examples 1-5 are as Figure 2 shown, reflecting the thermal properties of the samples. As Figure 2 can be seen, the unit B (4,4'-biphenylene ether dianhydride) containing ether is introduced into co-PI ABAC to ensure the thermal properties of the sample. At the same time, the two trifluoromethyl groups in unit C (hexafluorodiacid anhydride) reduce the free volume of atomic movement between units and restrict the free movement of molecules, thereby increasing the glass transition temperature T g of the material. Among them, the co-PI ABAC sample is improved compared with other comparative examples such as regular PI, and the ordered polymer T g (363 °C) is also higher than the disordered polymer r-co-PI T g (335 °C).

[0074] (2) The energy storage performance of the thin film sample is related to its dielectric constant and dielectric loss. The dielectric properties of the thin film samples prepared in Examples 1-3 and Comparative Examples 1-5 at 200 °C are as Figure 3 shown. Since polar groups are introduced into units A, B, and C, the dielectric constant of co-PI ABAC increases the most compared with other comparative examples, up to 3.9. And the dielectric loss basically remains at 10 2 ~10 6 level in the frequency range of 10 -3 . In addition, different types of polar groups are introduced into co-PI A’BA’C and co-PI A”BA”C , so the dielectric constant is also significantly increased compared with non-copolymers. However, due to too few or too many polar groups on the benzene rings of unit A' and unit A", the dipole loss of the polymer increases, so the dielectric loss of co-PI A’BA’C and co-PI A”BA”C is higher than that of co-PI ABAC .

[0075] (3)The energy storage performance of the thin film sample at 200 °C is as Figure 4 shown. Among them, co-PI ABAC , co-PI A’BA’C and co-PI A”BA”C at the high temperature of 200 °C, the maximum discharge energy density with a charge-discharge efficiency ≥ 90% U d90 are 5.53, 4.9 and 4.5 J•cm -3 respectively, which are significantly higher than those corresponding to the non-copolymer and disordered copolymer U d90 , indicating that the sequence combination and orderliness of polymer units have an impact on the energy storage performance of the material. From the results, it can be seen that ABAC is the best sequence combination, followed by A’BA’C and A”BA”C.

[0076] (4)The Weibull breakdown of the thin film sample at 200 °C is as Figure 5 shown. The Weibull breakdown strength is an important indicator to measure the electrical insulation performance of the sample. Among them, the orderliness of the copolymer effectively improves the Weibull breakdown strength of the material. Among them, the improvement effect of the Weibull breakdown strength of co-PI ABAC is the most significant, reaching 563 MV m -1 , co-PI A’BA’C and co-PI A”BA”C followed, with Weibull breakdown strengths of 548 MV m -1 and 539 MV m -1 respectively.

[0077] (5)The leakage current test results of the thin film sample at 200 °C are as Figure 6 shown, which reflects the insulation performance and electrical stability of the material. Among them, at 200 °C, due to the synergistic effect of the ether bond and the polar group trifluoromethyl in the unit segment, the structural stability of the material at high temperature is ensured, and at the same time, the electron migration excited by the thermal and electric field coupling is inhibited. Therefore, the leakage current quantity level of the corresponding co-PI ABAC is the lowest. For example, at 250 MV m -1 , 200 °C, the current density of co-PI ABAC is of the order of 10 -4 .

[0078] At the same time, the electron hopping distance in the material is calculated by fitting the hopping conduction model d . Among them, the smaller the hopping distance, the deeper the trap depth constructed, that is, the better the effect of inhibiting charge transport. Among them, the hopping distance fitted and calculated by co-PI ABAC is the shortest (d = 0.73 nm), co-PI A’BA’C and co-PI A”BA”CIt is also shorter than the hopping distances obtained by fitting non-copolymers and disordered copolymers, which are 1.19 and 1.20 nm respectively.

Claims

1. A sequentially arranged polyimide copolymer for a capacitor, characterized in that, The structural formula is as follows: Among them, X is selected from , , ; the preparation steps of the capacitor using the polyimide copolymer arranged in sequence include: (1) Under stirring conditions, a 4,4'-biphenyl ether dianhydride solution is dropped into a diamine monomer solution, and stirring reaction is carried out; the diamine monomer is one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, and 4,4'-(1,4-phenylene diisopropylidene)dianiline, and the molar ratio of 4,4'-biphenyl ether dianhydride to the diamine monomer is 1:2; (2) Hexafluorodiacid anhydride is added to the solution obtained in step (1) in portions, and the molar ratio of 4,4'-biphenyl ether dianhydride to hexafluorodiacid anhydride is 1:1; stirring reaction is carried out; (3) The solution obtained in step (2) is dried to evaporate the solvent, subjected to high-temperature treatment, and cooled to obtain a polyimide copolymer arranged in sequence for use in capacitors.

2. A method for preparing a sequentially arranged polyimide copolymer for a capacitor, characterized in that, It includes the following steps: (1) Under stirring conditions, a 4,4'-biphenyl ether dianhydride solution is dropped into a diamine monomer solution, and stirring reaction is carried out; the diamine monomer is one of 2,2-bis(4-aminophenyl)propane, p-phenylenediamine, and 4,4'-(1,4-phenylene diisopropylidene)dianiline, and the molar ratio of 4,4'-biphenyl ether dianhydride to the diamine monomer is 1:2; (2) Hexafluorodiacid anhydride is added to the solution obtained in step (1) in portions, and the molar ratio of 4,4'-biphenyl ether dianhydride to hexafluorodiacid anhydride is 1:1; stirring reaction is carried out; (3) The solution obtained in step (2) is dried to evaporate the solvent, subjected to high-temperature treatment, and cooled to obtain a polyimide copolymer arranged in sequence for use in capacitors; the high-temperature treatment is: reacting at 150 - 160 °C for 1 - 2 h, reacting at 200 - 210 °C for 1 - 2 h, and reacting at 250 - 260 °C for 1 - 2 h; the structural formula of the polyimide copolymer is as follows: Among them, X is selected from , , one of them.

3. The preparation method according to claim 2, characterized in that, In step (1), the solvent of the 4,4'-biphenyl ether dianhydride solution is N-methylpyrrolidone, and the concentration is 0.025 - 0.25 M; In step (1), the solvent of the diamine monomer solution is N-methylpyrrolidone, and the concentration is 0.05 - 0.5 M.

4. The preparation method according to claim 2, characterized in that, In step (1), the temperature of the stirring reaction is room temperature, and the time is 1 - 3 h.

5. The preparation method according to claim 2, characterized in that, In step (2), the temperature of the stirring reaction is room temperature, and the time is 1 - 3 h.

6. The preparation method according to claim 2, wherein In step (2), the hexafluorodiacid anhydride is added in 2 - 3 portions; In step (3), the drying temperature is 80 - 90 °C, and the time is 12 - 16 h.

7. The preparation method according to claim 2, wherein Before drying in step (3), the solution is poured on a glass plate; After cooling in step (3), it is soaked in cold water to separate the polyimide copolymer, and then dried.

8. Application of the polyimide copolymer arranged in sequence for use in capacitors according to claim 1 in the preparation of a high-temperature capacitor with a breakdown strength ≥ 550 MV / m and an energy storage density ≥ 5.5 J / cm³ at 200 °C.

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