High Discharge Energy Density Research Articles

Enhanced energy-storage density in silver niobate ceramics by Yb3+ doping at A-site

High energy density is an important factor for antiferroelectric materials applied in power pulse devices. Herein, the Ag(1-3x)YbxNbO3 (AYNO-100x) ceramics with x = 0, 0.02 and 0.04 were synthesized via a solid-state reaction method in an oxygen atmosphere. The Yb3+ doping at A-site reduces the oxygen vacancy and increases the silver vacancy after reaching saturation, which improves the antiferroelectric stability, leading to enhanced recoverable energy-storage density of 2.7 J/cm3 under 255 kV/cm at room temperature. Meanwhile, a relatively high discharge energy density of 1.0 J/cm3 at 200 kV/cm is also observed in the Ag0.94Yb0.02NbO3 ceramic. These results indicate that AgNbO3 -based ceramics are potential candidates in advanced power electronic devices.

Side-Chain-Type High Dielectric-Constant Dipolar Polyimides with Temperature Resistance.

Innovative dielectric materials with high-temperature resistance and outstanding dielectric properties have attracted tremendous attention in advanced electronical fields. Polyimide(PI) is considered a promising candidate for the modern electronic industry due to its excellent dielectric properties and comprehensive properties. However, the limited-adjustable range of dielectric constant and the difficulty to obtain a high dielectric constant restrict the application of PI as high dielectric materials. Herein, a novel diamine monomer (2,2'-bis((methylsulfonyl)methyl)-[1,1'-biphenyl]-4,4'-diamine (BSBPA)) containing a rigid biphenyl structure and high dipolar sulfonyl pendant groups is designed for high dielectric polyimides. The rigid biphenyl and polar sulfonyl pendant groups can reasonably optimize the molecular structure and orientational polarization of polyimides to improve their dielectric properties and thermal properties. Moreover, the effect of different bridge linkages on the dielectric properties is studied by using the different dianhydrides. Thus, the PI-BSBPA films especially the DSDA-BSBPA film (DSDA: 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride)achieve great thermal properties (T5%d of 377°C and Tg of 358°C) and excellent dielectric properties (6.95 at 1kHz) along with high discharged energy density of 5.25Jcm-3 and charge-discharge efficiency of 90%. The collaborative control of main-chain and side-chain engineering is effective to endow the polyimides with high-temperature tolerance and high dielectric performance.

High Energy Density of Polyvinylidene Fluoride‐Based Composite Films Induced by Anisotropic PLZT Fillers

AbstractWith the rapid development of electronic industry, high‐energy storage density dielectric materials are urgently needed to meet electronic components equipment miniaturized demand. Polymer dielectric materials have the advantages of good flexibility and high breakdown field, however, the energy storage capacity of polymers is limited by its inherent low dielectric constant. To improve the dielectric constant and energy storage density of the polymer material, we synthesized 0D (zero dimension), 1D, 2D lanthanum modified lead zirconate titanate (PLZT) fillers which introduced into polyvinylidene fluoride (PVDF) matrix. The anisotropic of the fillers has obvious improvement on the properties of materials. Compared with 0D fillers, high anisotropic fillers are more effective in enhancing the dielectric performances and energy density of PVDF based composites. The high anisotropic ratios of 2D fillers limit the charge migration toward the electrodes and hold back the growing electric tree during breakdown. Consequently, high breakdown strength (430 MV/m) and high discharge energy density (13.9 J/cm3) for 2D PLZT/PVDF composite films were obtained. This work is of critical significance in making dielectric capacitors for energy storage devices and reveals the influence mechanism for different dimensions fillers on the dielectric and energy storage properties of PVDF based composites.

High discharge energy density and ultralow dielectric loss in alkali-free niobate-based glass-ceramics by composition optimization

The SrO-BaO-Nb2O5-SiO2 glass-ceramics with different (Sr, Ba)/Nb ratio were prepared by the melting-crystallized process. With the decrease of (Sr, Ba)/Nb, the bonding species and crystallization activation energy of the glass-ceramics were changed obviously, which caused the change of phase compositions and microstructures on a microscopic scale and the fluctuations of dielectric constant and breakdown strength on a macroscopic scale. Finally, the theoretical energy storage density was up to 18.93 J/cm3 with a dielectric constant of 84 and breakdown strength of 2256.73 kV/cm. What is more, the dielectric loss was less than 0.004 at room temperature. Furthermore, under the electric field of 640 kV/cm the discharge energy density of the optimal sample (S5) reached 1.14 J/cm3 which overtopped what has been reported and the discharge time (t0.9) was less than 16 ns. Above analysis suggested that the alkali-free niobate-based glass-ceramics have broad application prospects.

All-polymeric multilayer para/ferroelectric dielectric films utilizing a gradient structure toward concurrent high discharge efficiency and energy density

Polymeric dielectrics exhibit huge prospects for power electronic devices due to their ultrafast charge-discharge speed. However, a persisting challenge is that enhanced energy density always brings about deteriorated efficiency. Herein, a novel design of all-organic dielectric films, consisting of gradient transition layers sandwiched between a paraelectric layer and a ferroelectric layer, are prepared. It is interesting to find that the breakdown behaviors of the multilayer films are strongly dependent on the configuration of gradient transition layers. Consequently, via adjusting the configuration of gradient transition layers, a high breakdown strength of 623 kV/mm, an excellent efficiency of 89.5%, along with a high-energy density of 7.34 J/cm3 are achieved. This work offers a unique route to develop polymeric dielectrics with concurrent high breakdown strength, high-energy density, and high efficiency.

High discharge energy density in novel K1/2Bi1/2TiO3-BiFeO3 based relaxor ferroelectrics

An increasing number of new dielectrics are being reported for the development of next-generation ceramic capacitors for power electronics used in clean energy technologies. Here, high discharge energy density (Wdis) ~6.1 J cm−3 with efficiency (η)~72% under a pulsed field (Emax) of 410 kV cm−1 is reported along with temperature stability up to 150 °C (Emax = 200 kV cm−1) for 0.5 K0.5Bi0.5TiO3-0.42BiFeO3-0.08Sm(Mg2/3Nb1/3)O3 (KBT-BF-SMN) bulk ceramics. The optimised composition is chemically heterogeneous but electrically homogenous, similar to several BiFeO3-based dielectrics reported previously and adding to the growing body of evidence that electrical (measured at weak-field) not chemical homogeneity is the best guide to increased Emax and enhanced energy density. KBT-BF-SMN ceramics are therefore considered as promising candidates for pulsed power and power electronics applications.

Boosting Energy Storage Performance of Lead‐Free Ceramics via Layered Structure Optimization Strategy

Owing to the current global scenario of environmental pollution and the energy crisis, the development of new dielectrics using lead-free ceramics for application in advanced electronic and energy storage systems is essential because of the high power density and excellent stability of such ceramics. Unfortunately, most of them have low breakdown strength and/or low maximum polarization, resulting in low energy density and efficiency. To overcome this limitation here, lead-free ceramics comprising a layered structure are designed and fabricated. By optimizing the distribution of the layered structure, a large maximum polarization and high applied electric field (>500kV cm-1 ) can be achieved; these result in an ultrahigh recoverable energy storage density (≈7 J cm-3 ) and near ideal energy storage efficiency (≈95%). Furthermore, the energy storage performance without obvious deterioration over a broad range of operating frequencies (1-100Hz), working temperatures (30-160°C), and fatigue cycles (1-104 ). In addition, the prepared ceramics exhibit extremely high discharge energy density (4.52 J cm-3 ) and power density (405.50 MW cm-3 ). Here, the results demonstrate that the strategy of layered structure design and optimization is promising for enhancing the energy storage performance of lead-free ceramics.

Supercritical Relaxor Nanograined Ferroelectrics for Ultrahigh-Energy-Storage Capacitors.

Supercritical relaxor nanograined ferroelectrics are demonstrated for high-performance dielectric capacitors, showing record-high overall properties of energy density ≈13.1 J cm-3 and field-insensitive efficiency ≈90% at ≈74kV mm-1 and superior charge-discharge performances of high power density ≈700 MW cm-3 , high discharge energy density ≈6.67 J cm-3 , and ultrashort discharge time <40ns at 55kV mm-1 . Ex/in situ transmission electron microscopy, Raman spectroscopy, and synchrotron X-ray diffraction provide clear evidence of the supercritical behavior in (Na,K)(Sb,Nb)O3 -SrZrO3 -(Bi0.5 Na0.5 )ZrO3 ceramics, being achieved by engineering the coexistence of multiple local symmetries within the ergodic relaxor zone. The vanished difference between the ground relaxor state and the high-field supercritical state eliminates polarization hysteresis. The supercritical evolution with electric field enables a highly delayed polarization saturation with continuously increased polarization magnitudes. The results demonstrate that such a design strategy of compositionally induced and field-manipulated supercritical behavior can be generalizable for developing desirable energy-storage dielectrics for applications in ceramic/film capacitors.

Combining covalent bonding interface among different components and controlled orientation of one-dimensional nanofibers for high energy density nanocomposites

Dielectric materials with high breakdown strength and excellent dielectric properties have attracted great attention because of their crucial importance in improving energy storage. In this study, a novel method for constructing covalent bonds at the interface of BaTiO3 nanofibers (BT NFs) and fluoropolymer to improve the interfacial adhesion is proposed, in combination with the orientation of one-dimensional BT NFs to improve the energy storage density. It was found that the cross-linked nanocomposites containing covalent bonding interface between thiol-modified BaTiO3 nanofibers (BT-SH NFs) and olefin-modified poly(vinylidene fluoride-chlorotrifluoroethylene) exhibited the supreme compatibility. In addition, the nanocomposite, in which the BT-SH NFs are oriented perpendicular to the electric field, is obtained by stretching, and its breakdown strength is increased by 7.1%. Consequently, the stretched nanocomposite with 5 vol% BT-SH NFs loading achieved a high discharged energy density of 17.1 J/cm3. The synergistic effect of cross-linking and stretching treatment accompanied by covalent bonding interface provides a novel strategy for manufacturing high-performance dielectric nanocomposites.

Crystallization temperature dependence of structure, electrical and energy storage properties in BaO–Na2O–Nb2O5–Al2O3–B2O3 glass ceramics

For dielectric capacitors, high energy density and discharge power density are crucial for utilisation in pulsed power devices. In this paper, BaO–Na2O–Nb2O5–Al2O3–B2O3 (BNN-AB) glass ceramics were successfully fabricated by melt quenching and heat treatment techniques. With increasing crystallization temperature, both the dielectric permittivity and breakdown strength (BDS) first increased and then decreased. When the crystallization temperature was lower than 800 °C, the principal crystalline phase was Ba2NaNb5O15 and the secondary phase was NaNbO3. When crystallization temperature was increased from 800 °C to 830 °C, a small amount of a third phase (Al4B2O9) appeared. At the crystallization temperature of 770 °C, the compact glass ceramics with a fine grain structure had the highest permittivity (∼216 @ 25 °C) and high BDS (∼1170 kV/cm). A single-layer capacitor made of glass ceramics had a high power density (∼414 MW/cm3) and discharge energy density (∼1.93 J/cm3), measured by the charge-discharge test platform under the applied field strength of 500 kV/cm. The discharge energy density of glass ceramics sample was as much as 7.7 times that of the mother glass. The above evidences indicate that BNN-AB glass ceramic materials have broad application prospects in the field of dielectric energy storage.

A Two-Dimensional Transient Model to Investigate the Influence of Flow Field Design on Zinc Deposition and Performance in a Zinc-Iodide Flow Battery

Zinc-based flow batteries are attractive because they have high aqueous solubility and hence high energy density, as well as rapid kinetics [1,2]. Among the aqueous redox flow batteries (RFBs), the zinc-iodide flow battery has been reported to have very high discharge energy density [1]. However, aqueous zinc batteries suffer from dendrite formation resulting in capacity fading and a decreased battery performance. In our previous study [3], we evaluated a novel flow field design for the zinc-iodide flow battery. When compared to a conventional flow-by (FB) mode, significantly higher charge and energy efficiencies were obtained with the novel arrangement. In the novel flow design, part of the was drawn through the porous electrode towards the current feeder, and this was found to enhance the effective surface area and decrease the ohmic loss. This design, called flow-by-through (FBT), with a component of flow in the direction of the current feeder, can prevent the blockage of the mass/ion transport pathway and enhance the flow distribution in hybrid flow batteries [4]. Based on X-ray computed tomography and SEM characterization, a denser zinc deposit, with more zinc deposition inside the felt were observed with the FBT mode, which may explain the increased discharge capacity and cycle life of the battery [3].A mathematical model of the zinc-iodide RFB can help us better understand the battery performance in the different flow modes. Models of RFBs have been used to investigate the impact of the flow field on performance since 1980 [5]. In this study, we have used a two-dimensional transient model with the COMSOL multi-physics software package to study the galvanostatic charge/discharge behavior of the zinc-iodide RFB in FB and FBT modes. The model considers the electrochemical kinetics, mass transport and the current and potential distribution in a single cell zinc-iodide flow battery. This is the first reported modeling study of the influence of the FBT design on the performance of an RFB.The galvanostatic charge-discharge of a zinc-iodide battery was modelled at a current density of 20 mA cm-2, and a charge duration of 20000 s, corresponding to a state of charge of 25.7%. These conditions were chosen to enable comparison and validation with experimental data are shown in Figure 1. The rate of zinc ion consumption and the amount of zinc deposition on the graphite felt electrode for both FB and FBT arrangements were evaluated using the model. The distribution of zinc deposition, potential and current, will be presented, which provide new insights into the impact of the flow arrangement on the battery performance. The model will be applied to predict cell voltage and efficiency, maximum discharge capacity and maximum discharge power density of the zinc-iodide RFB for FB and FBT arrangements.[1] Li, B., Nie, Z., Vijayakumar, M., Li, G., Liu, J., Sprenkle, V., & Wang, W. (2015). Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueous redox flow battery. Nature communications, 6(1), 1-8.[2] Higashi, S., Lee, S. W., Lee, J. S., Takechi, K., & Cui, Y. (2016). Avoiding short circuits from zinc metal dendrites in anode by backside-plating configuration. Nature communications, 7(1), 1-6.[3] ShakeriHosseinabad, F., Daemi, S. R., Momodu, D., Brett, D. J., Shearing, P. R., & Roberts, E. P. (2021). Influence of Flow Field Design on Zinc Deposition and Performance in a Zinc-Iodide Flow Battery. ACS Applied Materials & Interfaces, 13(35), 41563-41572.[4] Zhou, X., Lin, L., Lv, Y., Zhang, X., Fan, L., & Wu, Q. (2020). Elucidating effects of component materials and flow fields on Sn–Fe hybrid flow battery performance. Journal of Power Sources, 450, 227613.[5] Trainham, J. A., & Newman, J. (1981). A comparison between flow-through and flow-by porous electrodes for redox energy storage. Electrochimica Acta, 26(4), 455-469. Figure 1

Multi-cationic ionic liquid combination enabling 86-fold enhancement in frequency response and superior energy density in all-solid-state supercapacitors

Polymer ionic-conductor electrolytes with seamless electrode-electrolyte interface are indispensable for extracting the full potential of all-solid-state electrochemical double layer capacitors. While ionic liquids are among the best ionic conductors in liquid state and offer a wide potential window, translating their ionic mobility and activity to solid-state is important, yet challenging. In this direction, we report a mixed ionic liquid based solid electrolyte with an ionic conductivity of 1 mS/cm that delivers 86-fold higher scan-rate operability and 2.6 times lower relaxation time constant than their individual constituents. Specifically, a flexible polymeric matrix impregnated with a mixture of monocationic (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMIm TFSI)) and a dicationic ionic liquid (1,4-di(vinylimidazolium) butane bisbromide ([DVIM]Br)) facilitates rapid and extensive formation of electrical double layer when integrated with carbon-based electrodes. The resulting all-solid-sate flexible supercapacitor achieves superior scan rate operability (15,000 mV/s) and ultralow relaxation time constant (7.8 ms), translating to high discharge current density (>1 mA/cm2), energy density (26.4 Wh/kg) and power density (61,127 W/kg). The improved rate capability (~83 %) and energy storage performance is attributed to a synergistic interplay of ionic strength, conductivity and ion mobility of the mixed ionic-liquid that unfold newer avenues towards solid-electrolyte engineering for energy storage devices.

Enhanced Energy Storage Performance of PVDF-Based Composites Using BN@PDA Sheets and Titania Nanosheets.

With the rapid development of modern electrical and electronic applications, the demand for high-performance film capacitors is becoming increasingly urgent. The energy density of a capacitor is dependent on permittivity and breakdown strength. However, the development of polymer-based composites with both high permittivity (εr) and breakdown strength (Eb) remains a huge challenge. In this work, a strategy of doping synergistic dual-fillers with complementary functionalities into polymer is demonstrated, by which high εr and Eb are obtained simultaneously. Small-sized titania nanosheets (STNSs) with high εr and high-insulating boron nitride sheets coated with polydopamine on the surface (BN@PDA) were introduced into poly(vinylidene fluoride) (PVDF) to prepare a ternary composite. Remarkably, a PVDF-based composite with 1 wt% BN@PDA and 0.5 wt% STNSs (1 wt% PVDF/BN@PDA−STNSs) shows an excellent energy storage performance, including a high εr of ~13.9 at 1 Hz, a superior Eb of ~440 kV/mm, and a high discharged energy density Ue of ~12.1 J/cm3. Moreover, the simulation results confirm that BN@PDA sheets improve breakdown strength and STNSs boost polarization, which is consistent with the experimental results. This contribution provides a new design paradigm for energy storage dielectrics.

Concurrently Achieving High Discharged Energy Density and Efficiency in Composites by Introducing Ultralow Loadings of Core-Shell Structured Graphene@TiO2 Nanoboxes.

Polymer dielectrics have drawn tremendous attention worldwide due to their huge potential for pulsed power capacitors. Recent studies have demonstrated that linear/nonlinear layered composites, which can effectively balance energy density and efficiency, have huge potential for capacitive energy storage applications. However, further enhanced energy densities are strongly desired to meet the everincreasing demand for the miniaturization of electronic devices. Herein, a novel class of core-shell structured graphene@titanium dioxide nanoboxes is successfully synthesized and introduced into poly(vinylidene fluoride-hexafluoropropylene)-poly(ether imide) double-layer films. It is exciting to find that the introduction of merely 0.5 wt % nanoboxes results in a substantially enhanced energy density of 19.39 J/cm3, which is over 2.6 times that of the film without nanoboxes (7.44 J/cm3). Meanwhile, a high breakdown strength of 655 kV/mm and a high efficiency of 83% are achieved. Furthermore, the nanocomposites also show excellent power densities and cycling stabilities. These composites with excellent comprehensive energy storage performances have huge potential for advanced pulsed power capacitors.

Sandwich-structured polymer dielectric composite films for improving breakdown strength and energy density at high temperature

Polymer dielectric capacitor have attracted much attention in the field of electronic power systems recently due to high power density and high breakdown strength. However, with the development of miniaturization and integration, further demands have been set on the higher energy storage density as well as better temperature resistance for dielectric polymers. Up to now, hierarchical structure provides an effective way to meet these requirements. Herein, we report a sandwich-structured all-organic composite via inserting polymethyl methacrylate/poly(vinylidene fluoride) (PMMA/PVDF) blend layer into polyetherimide layers. Increasing temperature increases the permittivity of the middle layer and the addition of PMMA makes the permittivity increase faster with temperature than pure PVDF middle layer. The capacitor series model and finite element simulation confirmed that the change of the middle layer permittivity realized the electric field redistribution to self-adapt to the temperature, preventing premature breakdown at elevated temperature. At 100 °C, optimized composite exhibits a high breakdown strength of 486.05 MV/m along with high polarization. Eventually, a high discharge energy density of 8.65 J/cm3 is obtained, which is 229.44% of pure PEI. The high polarization at high temperature was realized by utilizing the permittivity of PMMA/PVDF rising with temperature, thereby increasing the energy density at elevated temperature.

Ultralow contents of AgNbO3 fibers induced high energy storage density in ferroelectric polymer nanocomposites

Polymer dielectric films have been widely used in electronic and power systems due to their unique dielectric properties, processing properties, and excellent cost performance. Although the dielectric constant of dielectric polymers can be improved by adding high contents of ceramic fillers, this approach comes at the expense of the breakdown strength (Eb). This work is inspired by the idea that high-aspect-ratio fibers can induce a larger electric dipole moment without sacrificing too much Eb compared to zero-dimensional nanoparticles, thereby effectively improving the energy storage performance of the composites. We synthesized antiferroelectric AgNbO3 (ANO) fibers by using an in situ topotactic transition reaction which were then introduced into the polyvinylidene fluoride (PVDF) matrix for energy storage applications. The results show that the nanocomposite film with an ultralow loading of 0.4 wt. % ANO fibers achieves a high discharge energy density of 12.97 J cm−3 at 490 MV m−1. Nanocomposites based on ultralow content ANO fibers show great promise as one-dimensional antiferroelectric fillers for high energy density capacitor applications.

Realizing enhanced energy density in ternary polymer blends by intermolecular structure design

Polymer nanocomposites have been extensively studied for dielectric energy storage applications, however, the relatively low breakdown strength due to inevitable defects and voids limits themselves in the development of the high energy density capacitors while large-scale manufacturing. Herein, we propose a facile strategy to improve the breakdown strength and thus energy density by synergistically designing the intermolecular structure in a ternary polymer blend composed of poly(methyl methacrylate), poly(vinylidene fluoride), and poly(vinylidene fluoride-hexafluoropropylene). We show that the appropriate quenching temperature can decrease crystal size and increase the fraction of the amorphous phase. Meanwhile, by designing the mass ratio of the ferroelectric poly(vinylidene fluoride) and poly(vinylidene fluoride-hexafluoropropylene), it will successfully introduce the intermolecular interaction, which stabilizes the γ-phase in ferroelectric polymers and leads to dense chain packing. All the phenomena contribute to the ultrahigh breakdown strength (850 MV/m), and the optimized blend exhibits a record high discharged energy density of 30 J/cm3. Of particular importance is that a large-area dielectric film with high property uniformity can be fabricated, demonstrating that the proposed design approach can be used as a general technology for mass production.

Outstanding discharge energy density and efficiency of the bilayer nanocomposite films with BaTiO3-dispersed PVDF polymer and polyetherimide layer

Dielectric polymer nanocomposite films have been widely studied because of their high polarization and electric breakdown strength, leading to high discharge energy density (Ud). However, nanocomposites with high Ud often show low discharge energy efficiency (η). In order to achieve both high Ud and η simultaneously, a series of novel bilayer polymer nanocomposite films composed of pure polyetherimide (PEI) layer and BaTiO3-dispersed poly(1,1-difluoroethylene) (BT/PVDF) layer were prepared by hot-pressing method in this work. The bilayer composites exhibit high η > 84% at 600 MV⋅m−1, which are much larger than most reported values (η < 70%). Specially, the highest η of 84.48% and Ud of 8 J·cm−3 at 600 MV·m−1 were obtained for the bilayer films composed of PEI and 3 vol% BT/PVDF layers, which is promising for pulsed power applications.

High-Performance PbZrO3-based antiferroelectric multilayer capacitors based on multiple enhancement strategy

Antiferroelectric (AFE) materials are thought to be one of the most promising candidates for energy storage application owing to their large polarization difference between maximum polarization and remanent polarization originating from unique electric field-induced phase transition, but the large polarization hysteresis leads to an inferior energy efficiency, which restricts their applications in advanced pulsed power devices. Herein, we propose a multiple enhancement strategy of composition and structural modification to solve this problem. The (Pb0.875La0.05Sr0.05)(Zr0.695Ti0.005Sn0.3)O3 (PLSZTS) antiferroelectric ceramic and corresponding multilayer ceramic capacitor (MLCC) are fabricated. A low hysteresis is obtained via composition optimization. Moreover, multilayer ceramic constructing improves significantly breakdown strength (BDS) due to decreased thickness of dielectric layer. An ultrahigh recoverable energy density (Wdis) of 19.9 J/cm3, together with a high energy efficiency (η) of 96.4% are achieved synchronously at an electric field of 85 kV/mm. In addition, the studied MLCCs also possess outstanding discharge energy storage properties with a high discharge energy density (Wdis) of 15.4 J/cm3 and a large power density (PD) of 170.5 MW/cm3, a wide temperature range of 20–120 °C, and strong fatigue endurance after 3000 cycles. The present research results not only offer a potential candidate for high-power energy storage devices, but also, more importantly, develop a universal approach for optimizing the overall energy storage performance.

Extremely low loading of carbon quantum dots for high energy density in polyetherimide nanocomposites

• Functionalized CQDs were synthesized, which showed monodispersity in solvent. • Coulomb-blockade effect of CQDs was utilized to increase the E b of PEI matrix. • The composite with 0.5 wt% CQDs exhibited a high U e of 10.66 J/cm 3 at 600 kV/mm. There is an urgent need for dielectric capacitors with high energy density and efficiency with the rapid progress of power electronic devices. Inorganic/organic composites were once considered as a potential candidate for dielectrics. However, the inevitable defects induced by the inorganic fillers always lead to the decreased breakdown strength and limited energy density and efficiency. In this work, carbon quantum dots (CQDs) with abundant functional groups were synthetized and introduced into linear dielectric polyethyleneimine (PEI) matrix. Due to the unique Coulomb-blockade effect of quantum dots, the movement of carriers can be hindered under the applied electric field, leading to the improvement of breakdown strength. Compared with most of the reported nanocomposites with high loading of fillers, the nanocomposites in this work with extremely low loading of CQDs exhibit obviously enhanced performance. The nanocomposite with 0.5 wt% CQDs exhibits a high discharge energy density of 10.66 J/cm 3 and efficiency of 88.3% at 600 kV/mm, corresponding to a 62.3% improvement over that of PEI (6.57 J/cm 3 at 490 kV/mm). This work provides an effective strategy to break down the long-standing contradiction between the enhancement of dielectric constant and the reduced in breakdown strength. The film dielectrics with extremely low loading of fillers contributing to enhanced energy density and high energy efficiency is very important for practical applications.