High‐energy‐density polymer nanocomposites with high‐dielectric‐constant ceramic nanoparticles as the reinforcement exhibit great potential for energy storage applications in modern electronic and electrical systems. However, the decline of breakdown strength by high loading of ceramic nanoparticles hinders this composite approach from sustainable promotion of energy density. In this work, an approach is proposed and demonstrated by constructing gradient distribution of the spherical ceramic nanoparticles in the polymer matrix. These gradient‐structured nanocomposites possess remarkably improved mechanical and electrical behaviors, which give rise to ultrahigh breakdown strength and much‐promoted energy density. Moreover, this enhancement effect can be further enlarged via increasing the grades number of gradient structures. This work provides an effective strategy for developing flexible high‐energy‐density polymer/ceramic nanocomposites for dielectric and energy storage applications.

High‐performance dielectric capacitors are critical for advanced electronics and electrical power systems. Polymeric dielectrics have been widely investigated for using in dielectric capacitors because of their high dielectric constants, flexibility, low density, and easy processability. However, it is still challenging to achieve simultaneous improvements in both energy density and efficiency in these dielectric polymers. Here, we report ferroelectric polyvinylidene‐fluoride‐based all‐organic dielectric polymer films with continuous compositional gradient structure are reported by modulating the spatial distribution of polymethyl‐methacrylate components, prepared via a facile and scalable additive manufacturing method. The continuous out‐of‐plane composition gradient in the all‐organic dielectric polymer films allows to tune electrical and mechanical behaviors, and thus induces a notably enhanced breakdown strength by modulating the electromechanical breakdown process related to the coupling of local electric field and stress. An ultrahigh discharge energy density of 38.8 J cm−3 along with a high discharge efficiency of >80% is achieved at the electric field of 800 kV mm−1 in the gradient polymer films, which is the highest energy density reported thus far in polymer‐based dielectrics including their nanocomposites and the highest energy efficiency achieved along with an energy density of >30 J cm−3.

Dielectric capacitors deliver the highest power density and operating voltage among known energy storage devices that are integrable in modern electronic and electrical systems. Ferroelectric polymers are promising dielectric energy storage media for film capacitors due to their superiority in excellent dielectric properties, high breakdown strength, and flexibility. Polymer-based nanocomposites by incorporating high-dielectric-constant nanofillers into the ferroelectric polymer matrix exhibit great potential for superior energy storage performances. This Perspective focuses on the development and progress of high-energy-density ferroelectric polymers and their nanocomposites. First, approaches are proposed to tune the ferroelectric hysteresis for suppressed dielectric and energy losses in ferroelectric polymers, which is the premise to achieve high energy density and high efficiency. Second, the energy storage properties of ferroelectric nanocomposites greatly depend on multiple factors such as nanofiller features, polymer/filler interfaces, and spatial composite structures, and effective strategies enabling enhancements of the dielectric constant and breakdown strength in nanocomposites are discussed. In the last part, some existing challenges and future perspectives are proposed to develop high-energy-density ferroelectric polymer-based materials for energy storage applications.

Ferroelectric polymers are the mainstay of advanced flexible electronic devices. How to tailor the ferroelectric polymer films for various applications via simple processing approaches is challenging. Here we demonstrate the tuning of ferroelectric responses can be achieved in polymer blends of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and polymethyl methacrylate (PMMA) prepared via a simple two-step process. The proposed two-step process endows the polymer blends with a random distribution of P(VDF-TrFE) crystalline phase, hence decoupling the coherent ferroelectric domain interactions between continuous ordered crystalline phases that ubiquitously existed in common P(VDF-TrFE) film. The incorporation of the miscible non-crystalline PMMA chains with low-polarity results in reversal dipoles and a transition from ferroelectric to antiferroelectric-like behavior, overcoming the trade-off between the polarization and depolarization fields. In particular, resultant excellent mechanical and electrical properties of the polymer blend films give rise to remarkably improved breakdown strength and energy storage performance, surpassing P(VDF-TrFE) and commercial biaxial-oriented polypropylene films. This work provides a simple and effective strategy to tailor the ferroelectric response of polymeric materials with great potential for flexible electrical energy storage applications.

Dielectric film capacitors with high power density and rapid charge–discharge capability are widely used as key components in modern electronic and electrical systems, and polymers are primary dielectric for film capacitors due to their low cost, flexibility, and ease of processing. Here, a surface engineering approach is reported to improve the energy storage properties of polymer films by directly spray coating 2D nanosheets on the polymer film surface. The spraying of 2D calcium niobate nanosheets on the surface of biaxially oriented polypropylene (BOPP) films leads to remarkably increased breakdown strength and dielectric constant, resulting in a maximum 64% enhancement of energy density compared to the pristine BOPP films. Ultraviolet irradiation is further employed to improve the adhesion of nanosheets to the BOPP film surface, leading to an ultrahigh energy density of 11.6 J cm−3 with a high energy efficiency of 90%, which is the highest energy density ever achieved in polypropylene‐based films. This work provides a universal, cost‐effective, and scalable approach to improve the energy density of dielectric polymer films, which is of great significance for the application of high‐energy‐density polymer films in compact and efficient power systems.