Dielectric Polymer Materials for Energy Storage Film Capacitors

Qitong Wang; Jiale Ding; Danying Zhao; Yunhe Zhang; Zhenhua Jiang

doi:10.7536/PC220615

Progress in Chemistry ›› 2023, Vol. 35 ›› Issue (1) : 168-176 DOI: 10.7536/PC220615

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Dielectric Polymer Materials for Energy Storage Film Capacitors

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Abstract

High power density, high charge-discharge efficiency, and long service life are important reasons why polymer film capacitors can be widely used in electric vehicles, smart grids and other electrical and electronic fields. Among them, dielectric polymer materials endow film capacitors with more possibilities due to their light weight, high breakdown strength, and easy large-scale processing. However, the low dielectric constant of dielectric polymers which results in the low energy density of the prepared capacitors, fails the material meeting the requirements of miniaturization and lightening of equipment. This paper summarizes the basic principles and performance parameters of dielectrics and film capacitors, and focuses on the introduction of dielectric polymer materials with energy storage as the main research direction, mainly including polymer-based nanocomposite dielectric polymers, dipole glass polymer materials, cross-linked dielectric polymers and multi-component all-organic dielectric polymers. Finally, we summarize the multiple challenges and potential opportunities faced by dielectric polymers in the process of fabricating energy storage capacitors with excellent performance.

Contents

1 Introduction

2 Polymer-based nanocomposites

2.1 0D inorganic particle and its surface treatment

2.2 1D and 2D inorganic fillers and their orientations

3 Dipolar glass polymers

4 Cross-linked dielectric polymers

5 Multicomponent dielectric polymers

5.1 Multi-layered multicomponent dielectric polymers

5.2 Blends

6 Conclusion and outlook

Graphical abstract

Keywords

polymer / capacitors / dielectric materials / nanocomposite

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Qitong Wang, Jiale Ding, Danying Zhao, Yunhe Zhang, Zhenhua Jiang. Dielectric Polymer Materials for Energy Storage Film Capacitors. Progress in Chemistry, 2023, 35(1): 168-176 DOI:10.7536/PC220615

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1 Introduction

With the depletion of traditional energy such as oil and coal, and the concern of the global ecological environment, the development and utilization of clean and renewable energy, mainly electricity, has become a research hotspot for researchers in the past decade. At the same time, the miniaturization, integration and high efficiency of devices have become the mainstream trend in the future development of electronic and electrical fields. At present, the most commonly used energy storage systems in the market are inductive energy storage, capacitive energy storage, mechanical energy storage and chemical energy storage. Therefore, as an energy storage element in passive devices, capacitors are also facing unprecedented challenges. Compared with other energy storage methods, capacitors have many advantages, such as fast charge and discharge speed (~ μs), long working life (10⁵~10⁶cycle), wide working temperature and frequency range, safety and reliability, which make them widely used in hybrid electric vehicles, energy power, pulse equipment and other fields^{[1⇓⇓⇓⇓⇓~7]}. However, the disadvantages of low energy storage density, large volume and heavy weight make it difficult for capacitors to meet the development requirements of miniaturization, integration and lightweight of equipment. Compared with traditional ceramic capacitors, dielectric polymer film capacitors have higher breakdown strength (MV·m^-1) and longer charge-discharge life, thus enabling capacitors to have higher energy density and reliability^[8⇓⇓~11]. Moreover, the specific slow failure mechanism of dielectric polymer film capacitors also allows them to operate effectively at higher applied electric fields^[12]. At the same time, compared with inorganic ceramic dielectric, dielectric polymer has the advantages of light weight, low price, easy processing and large-scale production^[3,13]. BOPP (biaxially oriented polypropylene) film, as the most widely used commercial dielectric polymer film material, has a low dielectric loss of ~ 0.0003, a high breakdown strength of more than >700 MV·m^-1, and a long service life of 20 000 H. However, because its dielectric constant is only 2.2, its energy density can only reach 1~2 J·cm^-3, which is far from the traditional electrochemical battery (20~29 J·cm^-3)^{[3,9,14⇓ ~16]}.

In order to improve the energy storage performance of dielectric polymer materials, the early research focused on using the percolation threshold theory to add conductive materials to improve the dielectric constant of materials^[7,17]. The percolation threshold theory holds that in a heterogeneous multicomponent system, near the percolation threshold, the system will undergo a transition from an insulating system to a metallic conductive system, because at this time, the conductive filler particles will form a continuous conductive network in the polymer matrix. For this reason, researchers at home and abroad have prepared composites with various polymers with different dielectric constants as the matrix and different types of conductive fillers (carbon, metal, etc.). However, after testing and characterization, it is found that although the dielectric constant of the composite with conductive filler has been significantly improved near the percolation threshold, the dielectric loss has also been significantly increased. At the same time, because the percolation threshold theory depends on the transition threshold of the material from insulator to conductor, with the addition of conductive materials, the conductivity of the composite increases, resulting in a significant decrease in the breakdown strength of the material. In general, the energy storage density of a dielectric material is calculated from

U = ∫ E d D

, where E is the applied electric field and D is the electric displacement. For a linear dielectric material, the above formula can be simplified to U=1/2DE=1/2ε₀ε_rE², where ε₀ is the vacuum permittivity and ε_r is the permittivity of the material. It is known that the composite prepared by adding conductive materials into the polymer matrix is not enough to meet the requirements of film capacitors. Therefore, how to maintain or even reduce the dielectric loss while improving the dielectric constant and breakdown strength, and prepare dielectric polymer materials with good comprehensive dielectric properties is the focus of current research.

This paper summarizes the research on improving the dielectric constant, reducing the dielectric loss and improving the breakdown strength from the polarization type and breakdown principle in order to improve the capacitance performance of materials in the past ten years.It mainly includes nano-composite dielectric polymer materials prepared by adding inorganic nano-fillers, dipolar glass dielectric polymer materials, cross-linked dielectric polymer materials, and multi-component dielectric polymer material. The effects of the dimension and spatial arrangement of inorganic fillers, the type and orientation of dipole groups, the bandwidth and the trap energy level on the comprehensive capacitance of the materials were discussed and summarized. Finally, the current difficulties and future challenges of high dielectric constant and low dielectric loss dielectric polymer materials are considered and discussed.

2 Polymer-based nano-dielectric polymer

2.1 0-dimensional (0-D) inorganic particle and its surface treatment

In order to solve the problem that the dielectric constant of pure resin polymer is generally low, researchers first thought of adding 0 D spherical inorganic ceramic particles (NPs, such as BaTiO₃, PbTiO₃, SrTiO₃, etc.) with high dielectric constant (10²~10⁴) into the polymer matrix to prepare nanocomposite dielectric materials. Mao et al. Prepared nanocomposites by adding 25 – 500 nm BaTiO₃ particles to the PVDF matrix to study the effect of filler size on the dielectric properties of the material^[18]. The dielectric constant of the nanocomposites with different sizes was significantly improved, and the dielectric constant of the nanocomposites with 100 nm BaTiO₃ particles was as high as ~ 100 (1 kHz).The dielectric constant of the nanocomposites is much higher than that of pure PVDF resin (~ 12,1 kHz), and the dielectric loss of the nanocomposites is also lower than that of pure PVDF resin without inorganic fillers, which indicates that inorganic fillers play an obvious role in improving the dielectric constant and reducing the dielectric loss of polymer materials. But at the same time, the addition of high dielectric constant inorganic fillers to the polymer matrix will also bring some problems. Firstly, due to the weak interfacial interaction between pure inorganic filler and polymer matrix, the dispersion of filler in the matrix is poor, even aggregation, which leads to the performance of nanocomposites can not be effectively improved, or even reduced. Secondly, compared with the ultra-high dielectric constant of inorganic fillers and the higher addition (20 vol% ~ 60 vol%), the dielectric constant improvement of nanocomposites is very limited^[3,19]. At the same time, due to the large difference between the dielectric constant of the inorganic ceramic filler and the polymer matrix, the electric field distortion will be caused under the applied electric field, which will induce the breakdown of the material prematurely, and also affect other properties of the material, such as thermal and mechanical properties^[17,20].

Therefore, in order to solve the problem of poor dispersion of inorganic particles in the polymer matrix, solve the problem of electric field distortion at the interface between the two, and at the same time, from the mechanism of dielectric response,Interfacial polarization also has an important contribution to the dielectric response of nanocomposites, so improving the interface between filler particles and polymer matrix has become the focus of research. At present, there are three kinds of interface treatment methods. The first kind is to prepare nanocomposites containing inorganic ceramic particles by in-situ polymerization^{[21⇓⇓~24]}. The nanoparticles in the nanocomposites prepared by in-situ polymerization have higher dispersion than the materials prepared by simple mixing, and the nanoparticles with different coating thicknesses can be prepared by adjusting the polymerization parameters. The second method is surface modification of nanoparticles^[25,26]. Kim et al. Used phosphonic acid to modify the surface of BTO, and the dielectric constant K of the nanocomposite prepared after modification can reach up to 37, while maintaining a low dielectric loss^[27]. What is more noteworthy is that the breakdown strength has been significantly improved compared with the unmodified nanocomposite. This is because the treatment of BTO particles by phosphonic acid on the one hand reduces the aggregation of filler particles after surface modification, and on the other hand reduces the concentration of ionizable hydroxyl groups on the surface of particles and the aggregation of mobile charges after surface passivation of fillers. On this basis, nanocomposites with double-layer core-shell structure can also be prepared, so that the effect of core-shell structure on the dielectric properties of materials can be better studied^[28,29]. The design idea of the interlayer of the double-layer core-shell nanocomposites is mainly to introduce materials with high dielectric constant (such as hyperbranched polyimide, HBP) or high conductivity materials (such as sodium polyacrylate, PANa). In this way, the polarity of the middle layer and the relative insulation of the outer shell can be simultaneously utilized, and the restriction on the dipole motion caused by the strong interaction between the general double-layer core-shell structure particle and the polymer matrix is avoided^[28].

The addition of metal to the polymer matrix in the percolation threshold range can effectively improve the dielectric constant of the composite, but due to the strong conductive properties of the metal, the dielectric loss is higher, and the breakdown strength of the composite is also reduced^[17]. However, when the diameter of some metal particles is reduced to a certain special size (≈10^-9m), these metal particles will show some special nano-size effects, such as quantum confinement effect as well as Coulomb blockade effect, and these effects can effectively enhance the dielectric properties of nano-dielectric composites, as shown in Fig. 1^[30,31].

The breakdown of the composite mainly occurs at the interface between the inorganic filler and the polymer resin. This is because at the interface, in addition to the dielectric mismatch, defects as well as impurities may cause charge accumulation, form leakage currents, and eventually initiate breakdown^[32]. Metal oxides (Al₂O₃, TiO₂) play a huge advantage in reducing the dielectric mismatch and suppressing the leakage current to improve the breakdown strength because of their relatively high dielectric constant (K ~ 10) as well as high bandwidth value (~ 9 eV)^[33⇓~35]. Therefore, the dielectric properties of the composites were significantly improved by simple blending, surface modification of metal oxide particles, or preparation of core-shell fillers^{[36⇓⇓⇓⇓~41]}. Guo et al. Prepared polymer-based composites containing inorganic ceramic particles (BTO) and metal oxides (TiO₂, ZrO₂) by in-situ polymerization and metallocene catalysis, respectively, and discussed the effects of inorganic particle size, morphology, and interfacial interaction on the dielectric properties of the composites, especially the leakage current^[42]. Compared with the nanocomposites with BTO particles, the nanocomposites with metal oxides have a more obvious reduction in leakage current. Ai et al. Used current density distribution simulation to further prove that metal oxide particles, especially Al₂O₃, have more obvious advantages in reducing material leakage current and improving breakdown strength, as shown in Fig. 2^[43]. It can be clearly seen from fig. 2 (e) that under the condition of the same content, the current density of the composite with the addition of Al₂O₃ particles is significantly reduced, and the dielectric properties of the composite are improved.It can also be confirmed by the results that the PI composite with Al₂O₃ particles has higher breakdown strength, energy storage density and charge-discharge efficiency (especially at high field) than the PI composite with HfO₂ and TiO₂ particles.

2.2 1D and 2D inorganic filler and their orientation

Compared with 0 D inorganic nanoparticles, 1 D nanofibers (NFs) and 2 D nanosheets (NPLs) have higher specific surface area, which can introduce more interfaces and improve the contribution of interfacial polarization to the dielectric constant of the composite^{[44⇓⇓~47]}. At the same time, due to the dimensional characteristics of inorganic particles (0 D), the breakdown path can easily pass through the filler particles and the polymer matrix from any direction, resulting in premature failure of the material. However, 1D nanofibers and 2D nanosheets (such as BNNs) can prevent the development and extension of the breakdown path under the electric field to a certain extent due to the dimensional advantage, so they can more effectively improve the breakdown strength of nanocomposites, as shown in Figure 3^[45,46]^[48⇓~50].

Similarly, for 1D nanofiber materials, the contradiction between high dielectric constant and high breakdown strength can be solved by preparing core-shell structure, adjusting the orientation of 2D fillers or 1D fiber fillers, and further adjusting the 3D distribution of fillers in the polymer matrix^[51⇓~53]^[45,54]^[55,56]. As shown in Fig. 4, the energy density of the BTO nanofiber/P (VDF-HFP) composite filled with the orthogonal orientation distribution is as high as 25.5 J·cm^-3 under the field strength of 690 kV·mm^-1, and the charge-discharge efficiency is maintained at 76.3%.

3 Dipolar glass dielectric polymer

Dipolar glass polymer is a kind of polymer with high glass transition temperature (T_g), in which strong dipolar groups are introduced into the main chain or side chain. This means that the chain motion of the polymer and the resulting dielectric/conductive losses are restricted, while the polar groups in the molecule can rotate, thereby enhancing the orientational polarization and increasing the dielectric constant. Unlike nanocomposites prepared by adding inorganic fillers to improve and perfect the interfacial polarization to obtain excellent dielectric properties, dipolar glass polymers are expected to use dipolar (oriented) polarization to prepare dielectric film materials with high dielectric constant and low dielectric loss. The preparation of dipolar glass polymer not only has a certain selectivity for strong dipolar groups, but also has certain requirements for the T_g and sub-T_g of the polymer. This is because the higher T_g can effectively reduce the electronic and ionic conduction in the material, and the sub-T_g is to ensure that the introduced dipoles can rotate relatively freely.However, it can not cause the overall movement of the polymer molecular chain segment, so as to ensure that the material will not cause the increase of dielectric loss while obtaining the increase of dielectric constant brought by the introduction of strong dipole groups^[57].

In recent decades, the research direction of dipolar glass dielectric polymers is mainly divided into two categories, one is the dipolar glass dielectric polymers with polar groups in the main chain, and the other is the dipolar glassy dielectric polymers with polar groups in the side chain. Backbone dipole glass dielectric polymer, as its name implies, is to connect different polar segments to the polymer backbone to add additional permanent dipoles to adjust the conjugation length and crystallinity in the molecular chain structure. It has been demonstrated that the introduction of strong dipolar functional groups, such as urea (— NH (C = O) NH —, ~ 4.5D), thiourea (— NH (C = S) NH —, ~ 4.9D), and nitrile (— CN, ~ 3.8D) into the main chain of the polymer can cause dielectric/conductive loss and thus affect the breakdown strength of the material^[58]^[59]^[60,61].

Treufeld et al. Introduced nitrile groups into the PI system, and found that the dielectric constant of PI with three strong dipole nitrile groups (~ 3.8) was higher than that of PI with only one nitrile group (~ 3.5) by adjusting the number of nitrile groups and the position of diammine (meta, para).Both of them have higher dielectric constant (~ 3.0) and higher dielectric loss (from 0.002 to 0.03) than the PI material prepared from 6FDA without nitrile group, which indicates that the introduction of nitrile group into the main chain can indeed improve the dielectric constant of the material without causing a sharp increase in dielectric loss^[60].

However, it can be seen from the results that the introduction of dipolar groups into polymers containing aromatic or heterocyclic main chains has limited improvement on the overall dielectric properties of the material, because as a part of the polymer main chain, even if the dipolar groups can rotate, the degree is limited after all. Therefore, researchers have begun to consider introducing strong dipole groups into the side chain to further improve the dielectric properties of materials by increasing the degree of freedom of dipole rotation and orientation^{[15,57,62⇓ ~64]}. It can be seen from fig. 5 that the highly rigid skeleton of the PPO matrix can provide enough rotation space for the mesyl group, improve the response ability of the dipole group to the applied electric field, and increase the orientation polarization, so that the dielectric constant can be improved while maintaining a low dielectric loss^[65].

On this basis, the effects of the number and position of sulfone groups on the dielectric properties and thermodynamic properties of the materials can be studied by adjusting the type of substituent groups (including monosulfone and bissulfone) and the number of substitution (monosubstitution and bissubstitution) of the introduced sulfone side groups^[66]. Sulfone or nitrile groups and other strong dipolar groups (such as vinyl pyrrolidone, VP) can be introduced simultaneously to increase the dielectric constant of the material to 8.0 (1 kHz) and maintain the dielectric loss at 0.016 (1 kHz)^[67]. The material can be crosslinked by simultaneously introducing a sulfone group and a crosslinkable epoxy side group, and the dielectric constant is improved by using a strong dipole group, and the dielectric loss is controlled and the breakdown performance is improved by using a crosslinked grid system^[62]. The side chain π-π stacking effect or the introduction of a liquid crystal phase structure can also be designed to form a short-range ordered structure within the molecule, which improves the orientation regularity of the dipole and thus improves the dielectric properties of the material, as shown in fig. 6^[68,69].

4 Cross-linked dielectric polymer

The breakdown strength of dielectric polymer materials is also very important to the overall performance of the capacitor. The comprehensive capacitance performance of the existing high temperature resistant dielectric polymer is not enough to meet the requirements of practical applications, in addition to the low dielectric constant, the breakdown strength caused by the leakage current is reduced. At high fields, leakage currents are formed by charges injected from the electrode plates and charges excited within the material itself. The existence of leakage current will not only seriously affect the breakdown strength E_b, but also produce the corresponding conduction loss and heat loss, and reduce the energy storage density U_e and charge and discharge efficiency η.

Crosslinking has been proved to be effective in improving the thermodynamic properties of thermoplastics by numerous researchers, and a considerable part of the work has shown that it is also successful in improving the breakdown strength of dielectric polymers and the performance of capacitors. This is because the cross-linked grid structure can hinder the generation and diffusion of leakage current, and also indirectly improve the breakdown strength of the material (electro-mechanical breakdown mechanism) by improving the mechanical properties of the material^{[62,70⇓⇓ ~73]}.

Zhang et al. introduced crosslinkable benzyne groups into polyetherimide oligomers and performed crosslinking treatment, and studied the effects of crosslinking conditions and crosslinking degree on the dielectric properties of the materials, as shown in Figure 7^[74]. Among them, the breakdown strength of c-10% PEPA-PEI material at 150 ℃ is increased from 400 MV·m^-1 of pure PEI resin to 500 MV·m^-1, and its high temperature energy storage density reaches 3.6 J·cm^-3 at 500 MV·m^-1, and maintains more than 95% of the charge-discharge efficiency. It is worth noting that the degree of crosslinking of benzyne group has a certain influence on the β relaxation of PEPA-PEI materials, that is, too low crosslinking degree can not effectively limit the secondary relaxation, while too high crosslinking degree will form defects, so the film materials with optimal crosslinking structure can show more excellent energy storage performance.

5 Multicomponent dielectric polymer

5.1 Multilayer dielectric polymer

The interface problem of dielectric polymer materials has always been one of the focuses of researchers. Although the interface provides a large amount of polarization charge, it is also the most vulnerable part to breakdown. In the monolayer nanocomposite system, the selection of filler particles, the surface modification method of particles, and the dimension and orientation are all to improve the contribution of interfacial polarization to the dielectric properties, while reducing the possibility of breakdown at the interface as much as possible. To this end, researchers have gone further to prepare multilayer dielectric polymers to complete the dual design of mixed molecular structure and interface at the same time, and to obtain dielectric polymer materials with better dielectric and capacitive performance^{[75⇓⇓⇓~79]}.

Pan et al. Designed and prepared a NN/PVDF nanocomposite dielectric material containing two-dimensional NaNbO₃ sheets by using the sandwich structure to adjust the dielectric difference between different layers and the advantage of 2D filler in inhibiting the development of breakdown path^[80]. The effect of the content of NaNbO₃ sheet on the overall dielectric properties of the nanocomposites was observed and discussed by adjusting the content of 2D filler in the upper and lower layers of the composites. The results show that the addition of NaNbO₃ sheets to the upper and lower layers of the sandwich structure can effectively improve the dielectric constant and control the dielectric loss of the composite. When the content of NaNbO₃ flakes in the upper and lower layers was 5 vol%, respectively, the energy storage density of the composite was as high as 13.5 J·cm^-3 at the intensity of 400 MV·m^-1, while it also possessed more excellent energy density (2.68 MW·cm^-3) and discharge rate (0.127 μs).

Sun et al. Prepared a three-layer all-organic composite film (LTN-Structure) with an asymmetric Structure by using PEI as the linear dielectric layer (L-layer), PEI/P (VDF-HFP) mixed film as the transition layer (T-layer), and P (VDF-HFP) as the nonlinear dielectric layer (N-layer), and carried out a series of characterizations and tests on its micro-morphology and capacitance performance (Fig. 8)^[81]. The results show that the three-layer composite film with the structure of E-20% E/F-F exhibits an energy density up to 12.15 J·cm^-3, and its charge-discharge efficiency is maintained at 89.9%. The researchers have designed experiments to prove that L-layer ensures the charge-discharge efficiency of the material, N-layer provides a higher energy density, and the existence of T-layer can adjust the electric field distribution between different layers, enhance the breakdown strength of multilayer film materials, thereby improving their energy storage density.

5.2 Dielectric polymer mixture

In order to improve the dielectric constant of dielectric polymers by dipole (orientation polarization), a certain amount of dipole groups must be introduced into the molecular structure. However, the coupling effect between adjacent strong dipoles will cause very obvious relaxation loss, so it is necessary to keep a certain distance between dipoles. Compared with polymer modification synthesis, which requires a large amount of work and a more cumbersome process, it is also a more appropriate way to select the appropriate polymer for mixing^[76,82]. Thakur et al. Prepared a dielectric polymer mixture by mixing two polymers that were not completely compatible and contained a strong dipole structure^[82]. The mixed polymer will have a certain mismatch in the chain segment scale, which will increase the chain spacing and free volume, and provide a certain rotation space for the dipole originally limited by the molecular glass state, thus improving the dielectric properties of the mixed polymer^[82].

In order to improve the breakdown strength of materials, it is necessary to effectively control the excited charge formed by electric field excitation and electrode injection. The cross-linked grid system reduces the leakage current and improves the breakdown strength of the material by forming and increasing the charge traps inside the material to capture the mobile charges. Therefore, the comprehensive properties of materials can be improved by directionally selecting some substances with high electron affinity or wide band gap to prepare all-organic dielectric polymers^[83,84].

Zhang et al. Introduced the radical trapping agent 2,2,6,6-tetramethylpiperidine oxide (TEMPO) to prepare an all-organic PNB-D_xT_y polymer (Fig. 9)^[85]. The breakdown strength of the prepared polymer can be up to 700 MV·m^-1, the charge-discharge efficiency can still be maintained at 92% at 500 MV·m^-1, and the energy storage density can be as high as 10.6 J·cm^-3. Moreover, compared with the complex process of adding inorganic fillers to prepare nanocomposites, this kind of all-organic dielectric polymer mixture is easier to process and produce on a large scale.

6 Conclusion and prospect

Whether it is sophisticated heavy industry or common light electronic and electrical equipment in daily life, the demand and requirements for capacitors are constantly increasing. Scientific researchers are also making continuous efforts to meet or even surpass these requirements. Dielectric nanomaterials based on inorganic nanoparticles/polymer resins have achieved exciting capacitive energy storage properties, but the preparation methods of these materials are relatively time-consuming, in addition to cumbersome steps.In addition to the incompatibility with the melt extrusion process currently used in large-scale production, the interface problem between filler particles and resin matrix has not been well solved, and the mechanism involved has not been discussed and summarized in depth and effectively. Dipolar glass polymers containing strong dipoles and multilayer dielectric composites also fail to achieve a satisfactory overall dielectric performance due to either a lower dielectric constant than expected or a lower breakdown strength. By summarizing the main problems of the above materials, it can be found that the leakage current in the polymer is an important factor affecting the capacitance performance of the whole material, especially in high field, because the leakage current will not only reduce the energy storage density and charge-discharge efficiency of the material, but also significantly reduce the breakdown strength. To this end, researchers have significantly improved the problem of generally low breakdown strength of dielectric polymers at high fields by designing crosslinking networks, adding free radical scavengers, and even adding low content of semiconductor materials to capture injected charges and excite charges to prevent the generation of leakage current.

In the past decade, dielectric polymers have made great progress in energy storage, but we still need to explore new molecular structures and segment structures to solve the balance problem between high dielectric constant, low dielectric loss and high dielectric stability of dielectric polymer materials. Multi-scale theoretical models and advanced nano-imaging techniques can also help us better understand the development process and mechanism of materials in application. Although there are still many scientific and technical problems to be solved, dielectric polymers still show great potential as one of the capacitor components under extreme conditions.

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