Polymer‐based capacitors with high energy density have attracted significant attention in recent years due to their wide range of potential applications in electronic devices. However, the obtained high energy density is predominantly dependent on high applied electric field, e.g., 400–600 kV mm ⁻¹ , which may bring more challenges relating to the failure probability. Here, a simple two‐step method for synthesizing titanium dioxide/lead zirconate titanate nanowire arrays is exploited and a demonstration of their ability to achieve high discharge energy density capacitors for low operating voltage applications is provided. A high discharge energy density of 6.9 J cm ⁻³ is achieved at low electric fields, i.e., 143 kV mm ⁻¹ , which is attributed to the high relative permittivity of 218.9 at 1 kHz and high polarization of 23.35 µC cm ⁻² at this electric field. The discharge energy density obtained in this work is the highest known for a ceramic/polymer nanocomposite at such a low electric field. The novel nanowire arrays used in this work are applicable to a wide range of fields, such as energy harvesting, energy storage, and photocatalysis.

Dielectric polymer materials have received increasing attention in the electronic and electrical industries, however, the miniaturization and intelligent applications of polymer capacitors are limited due to their low energy density. Recently, the construction of sandwich structured films provides a good pathway to improve the energy storage performance of dielectric polymers. In this research, all-organic sandwich structured dielectric polymer films consisting of linear dielectric and ferroelectric polymers are proposed and successfully made by simple layer-by-layer solution casting. Theoretically, the ferroelectric poly(vinylidene fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVTC) layer can enhance the dielectric displacement because of high dielectric constant, while the polyetherimide (PEI) layers can raise the operating temperature, owing to the high glass transition temperature, and increase the breakdown strength (E_b) and reduce the loss due to their linear characteristic. Therefore, a series of positive-sandwich structured films (with the central PVTC layer and the outer PEI layers), reverse-sandwich structured films and single-layered blend films are fabricated for optimization and comparison. The influence of the linear/ferroelectric volume ratio and the polymer film structure on the energy storage performance has been thoroughly researched. Experimental results showed that the all-organic positive-sandwich structured film with an optimized low content ratio of PVTC can endure a highest E_b of 530 kV mm⁻¹ and exhibits a maximum discharge energy density of 8.0 J cm⁻³, which was more than two times that of the pure PEI film. Furthermore, the efficiency was up to 81%. More importantly, it possesses excellent temperature stability of the dielectric and energy storage properties from 25 °C to 100 °C. This work provides theoretical analysis and experimental guidance for the fabrication of all-organic sandwich structured films with high energy storage performance, which promotes the development and application of flexible polymer high temperature dielectric capacitors.

Capacitor dielectrics with high energy density are urgently needed in power electronics and pulsed power system applications. To date, the most explored ceramic/polymer nanocomposites still suffer from the common challenge of a contradictory relationship between permittivity and the electric breakdown strength due to the overloading of nanofillers. Orientated films are considered the most prospective and scalable manufacturing option to overcome the above problems. Herein, a series of stretched PVDF polymer films were fabricated, and they demonstrated a substantial and concurrent increase in both electric displacement and breakdown strength (e.g. 16.10 μC cm⁻² at 798.8 kV mm⁻¹) by tuning its crystallization behavior in multiaspects. The phase transition and crystal orientation led to enhanced electric polarization, while the high strain-induced enhancement of Young's modulus and suppression of leakage current brought significant improvement in electric breakdown strength. Particularly, the effects of crystalline morphologies and orientations on the electric polarization behavior and stress distribution under high electric fields have been revealed by theoretical simulation, for the first time. As a consequence, the stretched PVDF films at a high strain of 500% (R = 5) almost presented the highest discharge energy density of 34.90 J cm⁻³ among dielectric polymers, along with a high energy efficiency of 68.2%, based on the solid-state drawing process. This work provides a feasible and paradigmatic approach to developing high-performance dielectrics for electrostatic energy storage applications.

A significant improvement of permittivity and energy density will enable the miniaturization of dielectric capacitors and promote integration for applications in electrical power and defense systems. In this work, lamellar composite architectures are fabricated from aligned barium titanate (BaTiO₃) in an epoxy resin using the freeze casting method. Due to the continuous coupling effect originating from the interconnected and highly oriented BaTiO₃ particles, these composites exhibit an extremely high permittivity (ε_r = 1408) at 1 kHz, which is the highest value achieved in BaTiO₃/polymer composites reported so far and fits well to the parallel mode of the mixing rule. A finite element model is used to investigate the local electric field distributions in the BaTiO₃ lamellae under the applied electric field parallel and perpendicular to the freezing direction, respectively. A high ratio value of discharge energy density per electric field, U_dis/E, ∼0.033, is achieved due to a high electric displacement of D = 15.11 μC cm⁻² and a discharge energy density of U_dis = 19.6 × 10⁻² J cm⁻³ is achieved at a low electric field (6 kV mm⁻¹). This work provides an effective strategy of designing a ceramic–polymer composite to realize high permittivity and energy density of capacitors for modern electrical and electronic industries.