Editorial: Dielectric materials for electrical energy storage

High-power energy storage systems have important applications in electrical grid, electric vehicles, nuclear, aerospace, telecommunication, military, defense and medical fields. The fast development of these equipment and devices drives the demand of new dielectric materials with high electrical energy storage capability. One may increase the energy density of dielectric materials via enhancing the dielectric constant and/or breakdown strength of the dielectric materials. Polymers have the advantages of lightweight, ease of processing, large scalability and high breakdown, but suffer from low dielectric constant. Most of the commercially available dielectric polymers have a dielectric constant lower than 10. The most commonly used metalized biaxially oriented polypropylene (BOPP) capacitors have a high breakdown strength of > 700 MV/m, but have low energy density because of the low dielectric constant. Therefore, new polymers with both high dielectric constant and high breakdown strength is highly desirable. Ceramics materials can have high dielectric constant and high temperature performance, whereas their applications for high energy density storage are restricted because of the low breakdown strength. The key to increasing the energy density of ceramic capacitors is to enhance the breakdown strength without significant decrease of their dielectric constant. Composite materials can utilize the advantages of each component. One may fabricate high-energy-density composites by incorporating high-dielectric-constant ceramic articles into high-breakdown-strength polymers. More importantly, the polymer composites also have the other advantages of the polymers, such as lightweight and ease of processing. In fact, such a strategy has been extensively used in the development of t1exible dielectric materials for electrical energy storage. The main challenge is to increase the dielectric constant of composites without significant decrease of their breakdown strength. Dielectric polymer nanocomposites (also called "nanodielectrics") exhibit great potential in developing high energy density materials, which can be fabricated by introducing high-dielectric-constant nanofiller (nanoparticles, nanofibers or nanosheets) into an insulating polymer matrix. It is a great pleasure that the articles in this special issue cover all these three topics and provide insight into the aforementioned trends. Many authors have the background of materials science or polymer science and provide interdisciplinary perspectives to readers of the Transactions.