With the rapid development of high-power electronic devices, pulsed-power systems, and advanced power-electronic technologies, dielectric capacitors are facing increasingly stringent requirements in terms of high energy density, high charge-discharge efficiency, and long-term operational reliability^[1-5]. Polymeric dielectrics play an important role in electrostatic energy storage because of their high dielectric strength, low loss, fast switching characteristics, and good processability. However, the commercial standard, biaxially oriented polypropylene (BOPP), is strictly limited by its insufficient dielectric constant. Because of this, the stored energy density within these linear polymers generally saturates under 2-3 J/cm³, which falls short of the rigorous demands for compact and high-integration electronic systems^[6,7].

Poly (vinylidene fluoride) (PVDF)-based relaxor ferroelectric polymers exhibit high dielectric constant and strong polarization, mainly because the highly polar C-F bonds provide large dipole moments along the polymer chains, giving these materials considerable potential for high-energy-density energy storage^[8,9]. However, PVDF-based materials typically contain large ferroelectric domains and pronounced crystalline structures, which tend to result in high remanent polarization and dielectric loss. Meanwhile, conduction loss and local electric-field concentration effects can significantly reduce the breakdown strength, thereby constraining the simultaneous improvement of discharged energy density and charge-discharge efficiency^[10,11]. Therefore, achieving a balance between maintaining high effective polarization while suppressing remanent polarization and charge-carrier transport has become a central challenge in the design of PVDF-based dielectric energy-storage materials.

In recent years, all-organic polymer blending has been regarded as an effective strategy that balances property regulation with processing feasibility. Previous studies have shown that introducing linear polymers into PVDF-based systems can, to some extent, suppress the growth of ferroelectric domains, reduce remanent polarization, and enhance breakdown strength^[12,13]. For example, Han et al. achieved uniform dispersion of polypropylene (PP) in PP/PVDF blends by regulating the phase structure and crystallization kinetics during processing, and further constructed a sandwich architecture to mitigate hysteresis loss. The resulting film delivered a discharged energy density of 8.1 J/cm³ and an energy-storage efficiency of 75%, indicating that the introduction of a small amount of a nonpolar phase can improve discharge efficiency without markedly sacrificing polarization^[14]. Luo et al. prepared poly(vinylidene fluoride- trifluoroethylene-chlorofluoroethylene)/poly(methyl methacrylate) [P(VDF-TrFE-CFE)/PMMA] films by blending and thermoforming, and obtained a discharged energy density of 11.2 J/cm³ with an efficiency of 85.8% at 4,750 kV/cm. Their results suggested that interfacial interactions, chain entanglement, and phase morphology play important roles in narrowing the polarization-electric field (P-E) loops and improving performance^[15]. Nevertheless, most existing studies have focused on macroscopic performance optimization. A systematic understanding of molecular-scale dipolar interactions, crystallinity evolution, and their coupled effects on energy-storage behavior is still lacking, especially in relaxor ferroelectric polymer systems.

To elucidate the relationship between microstructural features and macroscopic energy-storage performance in all-organic polymer blends, poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)] is used as the relaxor-ferroelectric matrix. PMMA, which possesses good insulation capability and chemical stability, is introduced as a modifying component to construct P(VDF-TrFE-CFE)/PMMA blend films. By tuning the PMMA content, we systematically investigate its influence on crystallization behavior and energy-storage properties. At a P(VDF-TrFE-CFE)/PMMA mass ratio of 50/50, the blend achieves a discharged energy density of 17.12 J/cm³ and an energy-storage efficiency of 88.11%, corresponding to increases of 53.9% and 64.2%, respectively, compared with pristine P(VDF-TrFE-CFE). In addition, the optimized film is subjected to γ-irradiation at different doses (10-150 kGy) to further explore the energy-storage potential of this system. Taken together, these results provide a useful structure-property framework based on molecular dipolar interactions and crystallinity regulation for the development of high-energy-density and high-efficiency all-organic dielectrics.

Figure 1 schematically illustrates the design concept of the P(VDF-TrFE-CFE)/PMMA blend films and the expected molecular-level interaction between the two components. The introduction of PMMA is expected to generate dipole-dipole interactions between the two components, which may affect chain packing, segmental mobility, crystallization behavior, and carrier transport in the blend films. Guided by this structural design, the following discussion examines the corresponding structural and electrical evolutions of the blend films through the relevant characterizations and correlates them with their dielectric, breakdown, and energy-storage behaviors.

Figure 2A shows the XRD profiles of neat P(VDF-TrFE-CFE), neat PMMA, and the blend films. The diffraction envelopes of the blend films progressively evolve from the neat P(VDF-TrFE-CFE) profile toward the broad amorphous halo of neat PMMA with increasing PMMA content. Since PMMA is an amorphous polymer, its incorporation drives the blend films toward a more amorphous-dominant structural state, leading to broader and more diffuse scattering features. At the same time, residual contributions associated with P(VDF-TrFE-CFE)-related ordering are still retained in the blend films. Therefore, the XRD evolution should not be interpreted as a simple shift of a single crystalline reflection. Instead, it reflects the combined effects of the increasing amorphous PMMA character and the suppression of residual P(VDF-TrFE-CFE) ordering^[15-19]. To further examine the internal structural evolution, both SAXS and WAXS analyses are performed [Figure 2B-F, Supplementary Figures 1 and 2]. No distinguishable scattering peak is observed in the SAXS profiles. The 2D SAXS patterns show diffuse scattering that attenuates radially from the center, indicating that PMMA blending does not induce a new periodic long-range ordered phase. The WAXS results show clear composition-dependent changes [Figure 2C-F and Supplementary Figure 2]. Compared with neat P(VDF-TrFE-CFE), the blend samples exhibit broader and more diffuse scattering characteristics. In particular, the 50/50 wt.% film shows a broader and more isotropic scattering ring in the 2D WAXS pattern [Figure 2E], indicating a more diffuse scattering distribution rather than a concentrated crystalline feature. Although its corresponding 1D profile in Figure 2C appears relatively strong, this should not be interpreted as a sharper crystalline reflection^[20,21]. Instead, it is better understood as a broadened scattering envelope that shifts away from the concentrated terpolymer-dominated feature toward a more amorphous character after blending. With further increasing PMMA content, the scattering feature becomes even more diffuse and gradually approaches the amorphous PMMA-like halo. Overall, the WAXS results indicate progressive broadening and redistribution of scattering with increasing PMMA content, consistent with suppressed crystallization and reduced short-range ordering in the films. The full-range FTIR spectra [Figure 2G] and the enlarged carbonyl (C=O) region [Figure 2H] show that, after blending, the characteristic carbonyl absorption band of PMMA shifts from ~1,724 cm^-1 in pristine PMMA to ~1,726 cm^-1 in the blend films, indicating that the local chemical environment of the carbonyl groups is altered after blending. In addition to this change, the absorption envelope in the 1,200-1,100 cm^-1 region also evolves significantly after blending, with the main band changing from ~1,174 cm^-1 in pristine P(VDF-TrFE-CFE) to ~1,149-1,144 cm^-1 in the blend films. Because this region contains overlapping contributions from PMMA and P(VDF-TrFE-CFE), the spectral evolution is more reasonably attributed to changes in the local environments of both components rather than to the shift of a single assigned bond. Meanwhile, the low-wavenumber fluoropolymer-related bands in the ~900-500 cm^-¹ region remain detectable, but also exhibit correlated changes in peak position and/or relative intensity after blending. This result further indicates that the local chain environments are affected by blending. Taken together, these FTIR results suggest that blending does not simply produce a physical superposition of the two components, but instead changes their local chemical environments. DSC is further employed to examine the thermodynamic features associated with crystallization [Figure 2I]. The pristine P(VDF-TrFE-CFE) film displays a pronounced endothermic melting peak, whereas none of the blend films shows such a melting endotherm; instead, only a single glass-transition temperature (T_g) is observed. Moreover, T_g shifts to higher temperatures with increasing PMMA content, indicating segmental mobility is progressively restricted. These results corroborate that crystallization is effectively suppressed and that the blends are predominantly amorphous^[22]. Meanwhile, the presence of a single T_g also supports the overall homogeneity of the blend system from a thermodynamic perspective^[23].

To better understand how the PMMA content influences the microstructure of the blend films, cross-sectional SEM and AFM characterizations are further performed on samples with different compositions [Supplementary Figures 3 and 4] to evaluate film continuity, compactness, and surface micro-morphology. The cross-sectional SEM images show that continuous film layers are formed for all compositions, with generally dense cross-sections and no obvious voids or through-thickness defects, providing a reliable morphological basis for the subsequent dielectric and high-field energy-storage measurements^[24,25]. AFM topography and corresponding amplitude images reveal microscale undulations and textured features on the surfaces of the films across different compositions. Overall, blending does not compromise the macroscopic structural continuity of the films^[12].

The dielectric constant and dielectric loss quantify a material’s capacity to store electrostatic energy and dissipate it under an applied electric field. Figure 3A and B display the dielectric spectra of P(VDF-TrFE-CFE)/PMMA blend films, illustrating how these properties vary with composition. With increasing frequency, the dielectric constant decreases for all samples. In contrast, the dielectric loss first decreases and then increases, a trend attributed to the inability of dipole reorientation to follow rapid field alterations at higher frequencies^[26]. Furthermore, the dielectric constant decreases monotonically with higher PMMA content. This reduction is linked to the amorphous structure of PMMA, where spontaneous dipole alignment is hindered, resulting in low macroscopic electroactivity. When incorporated into the P(VDF-TrFE-CFE) matrix, PMMA can reduce the overall polarization response in two ways^[27,28]. First, it dilutes the contribution from the highly polar fluorinated/chlorinated segments. Second, dipolar interactions between PMMA and P(VDF-TrFE-CFE) impose additional intermolecular constraints, which further suppress cooperative dipolar polarization. As a result, the dielectric constant decreases progressively as the PMMA fraction increases, and the corresponding dielectric constants at 10 kHz are summarized in Figure 3C. Regarding dielectric loss [Figure 3B and D], pristine P(VDF-TrFE-CFE) exhibits a noticeably higher loss across the entire frequency range, with a rapid increase at higher frequencies - an evolution commonly observed for relaxor ferroelectric polymers such as P(VDF-TrFE-CFE). With increasing PMMA content in the blend films, the dielectric loss in the high-frequency region is markedly suppressed.

Breakdown strength is a key determinant of the energy storage performance of polymer dielectrics; here, it is statistically assessed using a Weibull analysis of the film breakdown data. The Weibull distribution is expressed as:

(1) $$ X_{\mathrm{i}}=\ln \left(E_{\mathrm{i}}\right) $$

(2) $$ Y_{\mathrm{i}}=\ln (-\ln (1-i /(n+1))) $$

where n and i are the total number of samples and the sample serial number, respectively, with Eᵢ being the breakdown electric field of each specimen^[29]. The shape parameter (β), obtained from the slope of Xᵢ-Yᵢ linear fit, characterizes the dispersion of the breakdown data, and a high β value indicates greater reliability in the measured E_b. The E_b is defined by the intercept point of the fitted line at Y_i = 0. Figure 4A shows the Weibull statistical analysis of the breakdown strength for P(VDF-TrFE-CFE)/PMMA blend films with different PMMA contents. The overall linear fitting is satisfactory, indicating good reliability of the breakdown behavior. The corresponding characteristic breakdown strengths are summarized in Figure 4B. Introducing PMMA markedly enhances the breakdown strength, which increases from 5,120 kV/cm for pristine P(VDF-TrFE-CFE) to 7,500 kV/cm for the 70/30 wt.% blend. The representative unipolar P-E loops and corresponding energy-storage performance of the optimized P(VDF-TrFE-CFE)/PMMA 50/50 wt.% film are shown in Figure 4C, where a discharged energy density of 17.12 J/cm³ and an energy-storage efficiency of 88.11% are achieved while maintaining a high breakdown strength of 6,941 kV/cm. For comparison, the representative P-E loops of the other compositions are provided in Supplementary Figure 5. The enhanced electrical performance likely arises from several factors. PMMA itself is a linear polymer with high dielectric strength, which helps improve the electrical robustness of the blends. In addition, dipole-dipole interactions between the PMMA carbonyl groups and the polar groups in P(VDF-TrFE-CFE), together with altered chain packing and suppressed crystallization, may promote segmental confinement and hinder carrier transport^[30-34]. As an amorphous component, PMMA also disrupts the more continuous crystalline regions of P(VDF-TrFE-CFE), thereby blocking carrier-transport pathways and contributing to the increased breakdown strength^[34]. From the perspective of conduction behavior, enhanced breakdown strength is often accompanied by suppressed leakage current. Accordingly, the leakage current density and volume resistivity of the films are further measured under different electric fields [Supplementary Figure 6]. Compared with pristine P(VDF-TrFE-CFE), the PMMA-containing blends exhibit overall lower leakage current densities while maintaining higher resistivity, which is consistent with the view that the amorphous insulating PMMA matrix and the blend-specific heterointeractions help suppress carrier injection and transport. However, when the PMMA content is further increased, the breakdown strength of the blend films shows a slight decrease. This behavior may be related to excessive disruption of the residual ordered regions of P(VDF-TrFE-CFE) and the formation of local structural defects during thermal treatment, which could limit further improvement in breakdown strength.

Meanwhile, the maximum polarization (P_max) and remanent polarization (P_r) were evaluated, and the polarization difference (P_max-P_r) is used to represent the releasable polarization response during the charge-discharge cycle. As shown in Figure 4D, based on the P-E loops in Figure 4C and Supplementary Figure 5, although the P_max of some samples decreases compared with pristine P(VDF-TrFE-CFE) due to the incorporation of a large fraction of low-electroactivity PMMA, the P_r is also markedly suppressed. The resulting composition-dependent energy-storage performance is summarized in Figure 4E. Mechanical robustness can also influence the breakdown strength of the blend films. Figure 4F presents the Young’s modulus of films with different compositions. Pristine P(VDF-TrFE-CFE) exhibits a relatively low modulus of only 0.305 GPa, whereas the modulus increases markedly after incorporating PMMA and becomes significantly higher than that of pristine P(VDF-TrFE-CFE). Specifically, among the blend compositions, the modulus reaches 2.612 GPa for the 70/30 blend and then decreases to 2.377 and 2.134 GPa for the 50/50 and 40/60 blends, respectively, indicating a non-monotonic composition dependence. This behavior likely reflects a balance between the rigidifying contribution of PMMA and the progressive disruption of the residual ordered packing of P(VDF-TrFE-CFE) with increasing PMMA content. Accordingly, the 70/30 film appears to retain sufficient terpolymer-related structural continuity while already benefiting from the rigid PMMA component, giving the highest modulus among the blend films. With further increasing PMMA content, the increasingly amorphous blend structure offsets the stiffening effect of PMMA, leading to a decrease in modulus. Neat PMMA exhibits the highest modulus overall because it is a single rigid amorphous polymer, whereas the blend films are mechanically coupled two-component systems. Therefore, the enhanced breakdown strength cannot be attributed to mechanical stiffness alone, but should be understood as the combined result of mechanical robustness, crystallization suppression, reduced carrier transport, and improved structural homogeneity^[35].

Beyond high energy-storage capability, the stability and reliability of dielectrics are also critical performance metrics. Therefore, the P(VDF-TrFE-CFE)/PMMA 50/50 wt.% blend film, which exhibits the best overall performance, is selected to evaluate frequency stability and fatigue cycling stability at 3,000 kV/cm, and the results are summarized in Figure 5. The unipolar P-E loops measured at different frequencies from 50 Hz to 500 Hz are shown in Figure 5A, and the corresponding polarization parameters (P_max, P_r, and P_max-P_r) are summarized in Figure 5B. The discharged energy density, total energy density, and energy-storage efficiency are further compared in Figure 5C. Likewise, the fatigue-cycling behavior from 10⁰ to 10⁵ cycles is presented by the unipolar P-E loops in Figure 5D, with the corresponding polarization parameters summarized in Figure 5E and the related energy-storage performance shown in Figure 5F. Within the frequency range of 50-500 Hz and over 10⁰-10⁵ cycles, the unipolar P-E loops remain consistently slim. Across the tested frequency and cycling windows, the variations in U_e and η are only 6.2% and 2.5%, and 1.2% and 0.9%, respectively, indicating excellent frequency and cycling-reliability of the capacitive performance.

To further explore the energy-storage potential of this system, the P(VDF-TrFE-CFE)/PMMA 50/50 wt.% film with the best overall performance was subjected to γ-irradiation at different doses (10-150 kGy), and its structural and electrical responses are comparatively analyzed [Figure 6, Supplementary Figures 7 and 8]. From a structural perspective, the irradiated films remain dominated by a broad diffuse halo in the XRD patterns [Figure 6A]. No new crystalline diffraction peaks are observed after γ-irradiation. These results suggest that γ-irradiation does not induce the formation of a new crystalline phase and that the films still retain an amorphous-dominant structural feature. To further quantify the XRD evolution, the peak position of the broad diffraction feature is tracked as a function of irradiation dose [Supplementary Figure 9]. The feature gradually shifts from 16.25^o to 21.00 ^o, corresponding to a decrease in the calculated d-spacing from 5.45 Å to 4.23 Å. This result suggests that γ-irradiation affects the average spacing or local packing associated with this broad diffraction feature. Meanwhile, the FTIR spectra show a dose-dependent enhancement in the carbonyl-related absorption [Figure 6B], suggesting that oxidation-associated structural evolution is an important consequence of γ-irradiation in the present films^[36]. It should be noted, however, that the irradiation effect is unlikely to be limited to carbonyl formation alone. Based on previous reports on irradiated P(VDF-TrFE) polymers, γ-irradiation may also induce concurrent structural changes, including unsaturated structures, crosslinking in amorphous regions, and disordering or size reduction of crystalline regions. Such combined structural evolution may enhance dielectric performance through two main effects. First, the generation of additional polar oxygen-containing groups can strengthen dipolar polarization and increase the dielectric permittivity. Second, irradiation-induced disorder and constrained carrier transport can weaken ferroelectric long-range ordering, suppress remanent polarization and hysteresis loss, and reduce electrical dissipation, which helps maintain high energy-storage efficiency^[37,38]. In terms of electrical performance, at an irradiation dose of 100 kGy, the dielectric constant at 10 kHz increases from 5.58 to 8.75 [Figure 6C]. Meanwhile, a higher discharged energy density of ~28.14 J/cm³ is achieved, representing a 64.37% improvement over the untreated sample, while a high energy-storage efficiency of ~87.44% is still maintained [Figure 6D and Supplementary Figure 8]. These results indicate that 100 kGy provides the best balance between enhanced polarization response and reduced electrical loss, thereby leading to the optimal overall energy storage performance.

As shown in Supplementary Figure 10, the discharged energy density and efficiency achieved in this work are benchmarked against representative PVDF-based ferroelectric polymer systems reported in recent years^{[12,13,18,21,39-44]}. Many previously reported blend or composite strategies improve either energy density or efficiency, but achieving both simultaneously remains challenging. In particular, the incorporation of linear polymer components is often effective in enhancing breakdown strength and suppressing dielectric loss, whereas the corresponding reduction in dielectric constant and polarization response may limit the increase in discharged energy density. By contrast, ferroelectric-rich systems usually provide higher polarization but are often accompanied by larger hysteresis loss and lower efficiency. Compared with these representative systems, the P(VDF-TrFE-CFE)/PMMA blend developed in this work exhibits a more favorable balance between discharged energy density and efficiency. In particular, the optimized composition delivers high energy-storage performance while maintaining a relatively high efficiency, underscoring the effectiveness of all-organic blend design in regulating intermolecular interactions, crystallization behavior, and microstructure. These results demonstrate that the present strategy provides an effective route for developing high-performance polymer dielectrics for advanced capacitive energy-storage applications.

In this work, all-organic P(VDF-TrFE-CFE)/PMMA blend films were designed and fabricated to improve the energy-storage performance of polymer dielectrics through composition regulation and γ-irradiation treatment. The introduction of PMMA effectively modified the microstructure and electrical behavior of P(VDF-TrFE-CFE), leading to suppressed crystallization, enhanced breakdown strength, and improved energy-storage performance. Among the unirradiated blend films, the 50/50 wt.% composition exhibited the best overall performance, delivering a discharged energy density of 17.12 J/cm³ with an efficiency of 88.11%. Further γ-irradiation of this optimized blend film provided an additional performance enhancement, and the 100 kGy sample achieved a discharged energy density of 28.14 J/cm³ while maintaining a high efficiency of 87.44%. These results demonstrate that the combination of all-organic blending and irradiation engineering provides an effective strategy for developing high-performance polymer dielectric materials for advanced energy-storage applications.